U.S. patent application number 11/502390 was filed with the patent office on 2007-02-15 for tandem photosensitive-member unit for image-forming device.
This patent application is currently assigned to Brother Kogyo Kabushiki Kaisha. Invention is credited to Yasushi Okabe.
Application Number | 20070036582 11/502390 |
Document ID | / |
Family ID | 37742667 |
Filed Date | 2007-02-15 |
United States Patent
Application |
20070036582 |
Kind Code |
A1 |
Okabe; Yasushi |
February 15, 2007 |
Tandem photosensitive-member unit for image-forming device
Abstract
The tandem photosensitive-member unit includes a plurality of
photosensitive-member and a pair of side plates. The plurality of
photosensitive-member holding units each extends in a first
direction. The plurality of photosensitive-member holding units is
arranged in a second direction perpendicular to the first
direction. The pair of side plates each extends in the second
direction. The pair of side plates is disposed at both ends of the
arranged plurality of photosensitive-member holding units with
respect to the first direction. The tandem photosensitive-member
unit is configured to be detachably mounted as an integral unit in
a main body of an image-forming device.
Inventors: |
Okabe; Yasushi; (Nagoya-shi,
JP) |
Correspondence
Address: |
BANNER & WITCOFF, LTD.;ATTORNEYS FOR CLIENT NOS. 0166889, 006760
1001 G STREET, N.W., 11TH FLOOR
WASHINGTON
DC
20001-4597
US
|
Assignee: |
Brother Kogyo Kabushiki
Kaisha
Nagoya-shi
JP
|
Family ID: |
37742667 |
Appl. No.: |
11/502390 |
Filed: |
August 11, 2006 |
Current U.S.
Class: |
399/111 |
Current CPC
Class: |
G03G 21/181 20130101;
G03G 2221/1606 20130101; G03G 21/1676 20130101; G03G 15/0194
20130101; G03G 21/1853 20130101; G03G 21/1647 20130101; G03G
15/0189 20130101; G03G 2221/1846 20130101; G03G 2215/0119 20130101;
G03G 2221/1684 20130101 |
Class at
Publication: |
399/111 |
International
Class: |
G03G 21/16 20060101
G03G021/16 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 12, 2005 |
JP |
2005-234825 |
Dec 27, 2005 |
JP |
2005-376112 |
Claims
1. A tandem photosensitive-member unit comprising: a plurality of
photosensitive-member holding units each extending in a first
direction and holding a photosensitive member for each of a
plurality of colors, the plurality of photosensitive-member holding
units being arranged in a second direction perpendicular to the
first direction; and a pair of side plates each extending in the
second direction, the pair of side plates being disposed at both
ends of the arranged plurality of photosensitive-member holding
units with respect to the first direction, wherein the tandem
photosensitive-member unit is configured to be detachably mounted
as an integral unit in a main body of an image-forming device.
2. The tandem photosensitive-member unit according to claim 1,
wherein each photosensitive member has a shaft; and wherein the
pair of side plates comprises a shaft positioning part that
positions the shaft of each photosensitive member held in the
photosensitive-member holding unit.
3. The tandem photosensitive-member unit according to claim 2,
wherein the pair of side plates is formed with shaft holes at
positions corresponding to each shaft; wherein each shaft is
inserted into the respective shaft holes; and wherein the shaft
positioning part comprises: contact surfaces provided on peripheral
edges of the shaft hole, the peripheral edges being formed along
two imaginary intersecting lines; and an urging part that opposes
the shaft so that the shaft is interposed between the urging part
and the contact surfaces, the urging part urging the shaft toward
the contact surfaces.
4. The tandem photosensitive-member unit according to claim 1,
wherein the plurality of photosensitive-member holding units is
formed from a first material having a first coefficient of linear
expansion; and wherein the pair of side plates is formed from a
second material having a second coefficient of linear expansion
lower than the first coefficient of linear expansion.
5. The tandem photosensitive-member unit according to claim 4,
wherein the pair of side plates is formed from fiber reinforced
resin.
6. The tandem photosensitive-member unit according to claim 4,
wherein the pair of side plates is formed from metal.
7. The tandem photosensitive-member unit according to claim 1,
wherein the pair of side plates is provided with fitting parts that
slidably fits with guiding parts provided on the main body of the
image-forming device, thereby allowing the tandem
photosensitive-member unit to be slidably mounted in or removed
from the main body of the image-forming device.
8. The tandem photosensitive-member unit according to claim 1,
further comprising a pair of beam members spanning between the pair
of side plates, the pair of beam members being disposed at both
ends of the plurality of photosensitive-member holding units with
respect to the second direction.
9. The tandem photosensitive-member unit according to claim 8,
further comprising a grip part provided on at least one of the pair
of beam members.
10. The tandem photosensitive-member unit according to claim 1,
further comprising a developer unit mounted detachably on each of
the plurality of photosensitive-member holding units, the developer
unit holding a developer bearing member that supplies developer to
the photosensitive member.
11. The tandem photosensitive-member unit according to claim 10,
wherein the tandem photosensitive-member unit is mounted in and
removed from the image-forming device in the second direction;
wherein the urging part urges the shaft of the photosensitive
member in an urging direction that passes radially through an axial
center of the shaft; wherein each developer unit is mounted in the
tandem photosensitive-member unit in a mounting direction; and
wherein the urging direction is directed toward the same side as
the mounting direction with respect to an imaginary plane
perpendicular to the second direction.
12. The tandem photosensitive-member unit according to claim 10,
the pair of side plates is formed with a first insertion hole for
inserting a drive transmitting part, the drive transmitting part
transmitting a driving force from the main body of the
image-forming device to the developer unit.
13. The tandem photosensitive-member unit according to claim 10,
further comprising a charging unit held by each of the plurality of
photosensitive-member holding units, the charging unit charging the
photosensitive member, wherein each of the plurality of
photosensitive-member holding units comprising: a pair of side
frame sections that confronts each other with a distance
therebetween in the first direction; and a center frame section
that spans between the pair of side frame sections, the center
frame section supporting the charging unit along the first
direction.
14. The tandem photosensitive-member unit according to claim 13,
wherein the pair of side frame sections has a guide part that
guides the developer unit to be mounted in and removed from the
photosensitive-member holding unit.
15. The tandem photosensitive-member unit according to claim 13,
wherein each of the plurality of photosensitive-member holding
units includes a power supply part for applying a voltage to the
charging unit; and wherein the pair of side plates is formed with
an opening that exposes the power supply part toward outside of the
photosensitive-member holding unit in the first direction.
16. The tandem photosensitive-member unit according to claim 13,
wherein the pair of side frame sections is formed with a second
insertion hole for inserting a drive transmitting part, the drive
transmitting part transmitting a driving force from the main body
of the image-forming device to the developer unit.
17. The tandem photosensitive-member unit according to claim 13,
wherein each of the pair of side frame sections and the center
frame section is formed as a separate member.
18. The tandem photosensitive-member unit according to claim 13,
wherein the center frame section and at least one of the pair of
side frame sections are formed integrally.
19. The tandem photosensitive-member unit according to claim 18,
wherein at least one of the pair of side frame sections comprises:
a first division part formed integrally with the center frame
section; and a second division part formed separately from the
first division part.
20. The tandem photosensitive-member unit according to claim 19,
wherein the pair of side frame sections is formed with a second
insertion hole for inserting a drive transmitting part, the drive
transmitting part transmitting a driving force from the main body
of the image-forming device to the developer unit; and wherein the
first division part and the second division part are divided at the
second insertion hole.
21. The tandem photosensitive-member unit according to claim 17,
wherein the pair of side frame sections supports both ends of the
shaft; and wherein a plurality of pairs of side frame sections is
positioned relative to one another via the shaft.
22. The tandem photosensitive-member unit according to claim 13,
wherein the pair of side plates is formed with a rotation
restricting hole; and wherein the pair of side frame sections
comprises a rotation restricting part that is fitted in the
rotation restricting hole and that restricts rotation of the pair
of side frame sections about the shaft relative to the pair of side
plates.
23. The tandem photosensitive-member unit according to claim 22,
wherein the developer unit has a window that transmits a detection
light used to optically detect an amount of developer accommodated
in the developer unit; and wherein the rotation restricting part
has a cylindrical shape and confronts the window in a direction in
which the detection light is transmitted.
24. The tandem photosensitive-member unit according to claim 23,
wherein the pair of side frame sections is formed with a light
transmitting through-hole at a position opposing the window in the
direction in which the detection light is transmitted.
25. The tandem photosensitive-member unit according to claim 23,
wherein the pair of side plates is formed with a light transmitting
through-hole at a position opposing the window in the direction in
which the detection light is transmitted.
26. An image-forming device comprising: a main body; and a tandem
photosensitive-member unit configured to be detachably mounted in
the main body, the tandem photosensitive-member unit comprising: a
plurality of photosensitive-member holding units each extending in
a first direction and holding a photosensitive member for each of a
plurality of colors, the plurality of photosensitive-member holding
units being arranged in a second direction perpendicular to the
first direction; and a pair of side plates each extending in the
second direction, the pair of side plates being disposed at both
ends of the arranged plurality of photosensitive-member holding
units with respect to the first direction, wherein the tandem
photosensitive-member unit is configured to be detachably mounted
as an integral unit in the main body.
27. The image-forming device according to claim 26, wherein each
photosensitive member has a shaft; and wherein the pair of side
plates comprises a shaft positioning part that positions the shaft
of each photosensitive member held in the photosensitive-member
holding unit.
28. The image-forming device according to claim 27, wherein the
pair of side plates is formed with shaft holes at positions
corresponding to each shaft; wherein each shaft is inserted into
the respective shaft holes; and wherein the shaft positioning part
comprises: contact surfaces provided on peripheral edges of the
shaft hole, the peripheral edges being formed along two imaginary
intersecting lines; and an urging part that opposes the shaft so
that the shaft is interposed between the urging part and the
contact surfaces, the urging part urging the shaft toward the
contact surfaces.
29. The image-forming device according to claim 26, wherein the
plurality of photosensitive-member holding units is formed from a
first material having a first coefficient of linear expansion; and
wherein the pair of side plates is formed from a second material
having a second coefficient of linear expansion lower than the
first coefficient of linear expansion.
30. The image-forming device according to claim 29, wherein the
pair of side plates is formed from fiber reinforced resin.
31. The image-forming device according to claim 29, wherein the
pair of side plates is formed from metal.
32. The image-forming device according to claim 26, wherein the
main body has a guide part that guides mounting and removal of the
tandem photosensitive-member unit; and wherein the pair of side
plates has a fitting part that slidably fits with the guide part so
that the tandem photosensitive-member unit is slidably mounted in
and removed from the main body.
33. The image-forming device according to claim 26, wherein the
tandem photosensitive-member unit further includes a pair of beam
members spanning between the pair of side plates; and wherein the
pair of beam members is disposed at both ends of the plurality of
photosensitive-member holding units with respect to the second
direction.
34. The image-forming device according to claim 33, wherein the
tandem photosensitive-member unit further includes a grip part
provided on at least one of the pair of beam members.
35. The image-forming device according to claim 26, wherein the
tandem photosensitive-member unit further includes a developer unit
mounted detachably on each of the plurality of
photosensitive-member holding units; and wherein the developer unit
holds a developer bearing member that supplies developer to the
photosensitive member.
36. The image-forming device according to claim 35, wherein the
tandem photosensitive-member unit is mounted in and removed from
the image-forming device in the second direction; wherein the
urging part urges the shaft of the photosensitive member in an
urging direction that passes radially through an axial center of
the shaft; wherein each developer unit is mounted in the tandem
photosensitive-member unit in a mounting direction; and wherein the
urging direction is directed toward the same side as the mounting
direction with respect to an imaginary plane perpendicular to the
second direction.
37. The image-forming device according to claim 35, wherein the
pair of side plates is formed with a first insertion hole for
inserting a drive transmitting part, the drive transmitting part
transmitting a driving force from the main body of the
image-forming device to the developer unit.
38. The image-forming device according to claim 35, wherein the
tandem photosensitive-member unit further includes a charging unit
held by each of the plurality of photosensitive-member holding
units; wherein the charging unit charges the photosensitive member;
wherein each of the plurality of photosensitive-member holding
units comprising: a pair of side frame sections that confronts each
other with a distance therebetween in the first direction; and a
center frame section that spans between the pair of side frame
sections, the center frame section supporting the charging unit
along the first direction.
39. The image-forming device according to claim 38, wherein the
pair of side frame sections has a guide part that guides the
developer unit to be mounted in and removed from the
photosensitive-member holding unit.
40. The image-forming device according to claim 38, wherein each of
the plurality of photosensitive-member holding units includes a
power supply part for applying a voltage to the charging unit; and
wherein the pair of side plates is formed with an opening that
exposes the power supply part toward outside of the
photosensitive-member holding unit in the first direction.
41. The image-forming device according to claim 38, wherein the
pair of side frame sections is formed with a second insertion hole
for inserting a drive transmitting part, the drive transmitting
part transmitting a driving force from the main body of the
image-forming device to the developer unit.
42. The image-forming device according to claim 38, wherein each of
the pair of side frame sections and the center frame section is
formed as a separate member.
43. The image-forming device according to claim 38, wherein the
center frame section and at least one of the pair of side frame
sections are formed integrally.
44. The image-forming device according to claim 43, wherein at
least one of the pair of side frame sections comprises: a first
division part formed integrally with the center frame section; and
a second division part formed separately from the first division
part.
45. The image-forming device according to claim 44, wherein the
pair of side frame sections is formed with a second insertion hole
for inserting a drive transmitting part, the drive transmitting
part transmitting a driving force from the main body of the
image-forming device to the developer unit; and wherein the first
division part and the second division part are divided at the
second insertion hole.
46. The image-forming device according to claim 42, wherein the
pair of side frame sections supports both ends of the shaft; and
wherein a plurality of pairs of side frame sections is positioned
relative to one another via the shaft.
47. The image-forming device according to claim 38, wherein the
pair of side plates is formed with a rotation restricting hole; and
wherein the pair of side frame sections comprises a rotation
restricting part that is fitted in the rotation restricting hole
and that restricts rotation of the pair of side frame sections
about the shaft relative to the pair of side plates.
48. The image-forming device according to claim 47, wherein the
developer unit has a window that transmits a detection light used
to optically detect an amount of developer accommodated in the
developer unit; and wherein the rotation restricting part has a
cylindrical shape and confronts the window in a direction in which
the detection light is transmitted.
49. The image-forming device according to claim 48, wherein the
pair of side frame sections is formed with a light transmitting
through-hole at a position opposing the window in the direction in
which the detection light is transmitted.
50. The image-forming device according to claim 48, wherein the
pair of side plates is formed with a light transmitting
through-hole at a position opposing the window in the direction in
which the detection light is transmitted.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to Japanese Patent
Application No. 2005-234825 filed on Aug. 12, 2005, and Japanese
Patent Application No. 2005-376112 filed Dec. 27, 2005. The entire
content of each of these priority applications is incorporated
herein by reference.
TECHNICAL FIELD
[0002] The disclosure relates to a tandem photosensitive-member
unit and an image-forming device.
BACKGROUND
[0003] One type of tandem color laser printer well known in the art
includes four photosensitive drums and developing rollers for the
colors yellow, magenta, cyan, and black. In this type of tandem
color laser printer, the developing rollers form toner images in
each respective color on the photosensitive drums at substantially
the same time. Subsequently, the toner images are transferred onto
paper or an intermediate transfer belt, enabling color images to be
formed at approximately the same speed as an image formed on a
monochromatic laser printer.
[0004] One such tandem color laser printer proposed in U.S. Patent
Application Publication No. 2004/165910 (corresponding to Japanese
Patent Application Publication No. 2004-279551) includes developer
cartridges each with developing rollers, and drum units each having
a photosensitive drum such that the developing cartridges and drum
units can be individually mounted in or removed from a main casing
of the laser printer.
[0005] Another image-forming device disclosed in U.S. Pat. No.
6,738,590 (corresponding to Japanese Patent Application Publication
No. 2003-50531) has an image-forming unit in which are integrally
assembled a plurality of image-bearing members, a plurality of
developer units, a plurality of charging units, and at least one
intermediate transfer member. This integrated assembly can be
mounted in or removed from a main body of the image-forming
device.
SUMMARY
[0006] However, since the developer cartridges and drum units in
the image-forming device according to U.S. Patent Application
Publication No. 2004/165910 are mounted individually for each of
the colors yellow, magenta, cyan, and black, a total of eight
cartridges are replaced individually as consumables. With such a
large number of consumable parts, there is a danger that the user
may become confused and replace a cartridge with one of the wrong
color.
[0007] On the other hand, the image-forming unit of the
image-forming device disclosed in U.S. Pat. No. 6,738,590 is
mounted in and removed from the body of the image-forming device as
an integrated assembly, thereby preventing such confusion described
above as the user replacing the wrong cartridge. However,
manufacturing the image-forming unit as an integrated assembly
increases the complexity and cost of the manufacturing process and
also makes repairs inconvenient. The process of disassembling the
image-forming unit after use for recycling is also complex and
inconvenient.
[0008] In view of the foregoing, it is an object of the invention
to provide a tandem photosensitive-member unit having a simple
structure with a low number of consumable parts to prevent user
confusion in replacing such parts and that can reduce costs by
facilitating assembly and repair. It is another object of the
invention to provide a tandem photosensitive-member unit that is
suitable for recycling. It is another object of the invention to
provide an image-forming device in which the tandem
photosensitive-member unit is mounted.
[0009] In order to attain the above and other objects, according to
one aspect, the invention provides a tandem photosensitive-member
unit. The tandem photosensitive-member unit includes a plurality of
photosensitive-member and a pair of side plates. The plurality of
photosensitive-member holding units each extends in a first
direction and holds a photosensitive member for each of a plurality
of colors. The plurality of photosensitive-member holding units is
arranged in a second direction perpendicular to the first
direction. The pair of side plates each extends in the second
direction. The pair of side plates is disposed at both ends of the
arranged plurality of photosensitive-member holding units with
respect to the first direction. The tandem photosensitive-member
unit is configured to be detachably mounted as an integral unit in
a main body of an image-forming device.
[0010] According to another aspect, the invention provides an
image-forming device. The image-forming device includes a main body
and a tandem photosensitive-member unit. The tandem
photosensitive-member unit is configured to be detachably mounted
in the main body. The tandem photosensitive-member unit includes a
plurality of photosensitive-member holding units and a pair of side
plates. The plurality of photosensitive-member holding units each
extends in a first direction and holds a photosensitive member for
each of a plurality of colors. The plurality of
photosensitive-member holding units is arranged in a second
direction perpendicular to the first direction. The pair of side
plates each extends in the second direction. The pair of side
plates is disposed at both ends of the arranged plurality of
photosensitive-member holding units with respect to the first
direction. The tandem photosensitive-member unit is configured to
be detachably mounted as a unit in the main body.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Illustrative aspects in accordance with the invention will
be described in detail with reference to the following figures
wherein:
[0012] FIG. 1 is a side cross-sectional view showing a color laser
printer as an aspect of the image-forming device of the
invention;
[0013] FIG. 2 is a side cross-sectional view of a drum subunit
provided in the color laser printer of FIG. 1 on which a developer
cartridge is mounted;
[0014] FIG. 3 is a side cross-sectional view of the developer
cartridge shown in FIG. 2;
[0015] FIG. 4 is a perspective view from the left side of a drum
unit in which the developer cartridges are mounted;
[0016] FIG. 5 is a perspective view from the left side of a drum
unit in which one of the developer cartridges has been removed;
[0017] FIG. 6 is a plan view of the drum unit shown in FIG. 4;
[0018] FIG. 7 is a left side view of the drum unit shown in FIG.
4;
[0019] FIG. 8 is a cross-sectional view along a line VIII-VIII
indicated in FIG. 7;
[0020] FIG. 9 is an exploded perspective view of the drum
subunit;
[0021] FIG. 10 is a perspective view of the drum subunit;
[0022] FIG. 11 is a perspective view from the left side
illustrating the assembly of a pair of side plates to a front beam,
four drum subunits, and a rear beam in a juxtaposed
relationship;
[0023] FIG. 12A is a perspective view from the right side
illustrating the assembly of the pair of side plates to the front
beam, four drum subunits, and rear beam in a juxtaposed
relationship;
[0024] FIG. 12B is an enlarged view of FIG. 12A illustrating
electrodes;
[0025] FIG. 13A is a side view illustrating the positioning of drum
shafts in a side plate;
[0026] FIG. 13B is an enlarged view of FIG. 13A illustrating
portions near a wire spring;
[0027] FIG. 13C is an explanatory diagram showing how the wire
spring urges the drum shaft;
[0028] FIG. 14 is a perspective view from the left side
illustrating the pair of side plates that have been assembled to
the front beam, four drum subunits, and the rear beam in a
juxtaposed relationship;
[0029] FIG. 15A is a perspective view from the right side
illustrating the pair of side plates that have been assembled to
the front beam, four drum subunits, and rear beam in a juxtaposed
relationship;
[0030] FIG. 15B is an enlarged view of FIG. 15A illustrating
electrodes;
[0031] FIG. 16 is a rear view of the developer cartridge;
[0032] FIG. 17 is a left side view of the developer cartridge;
[0033] FIG. 18 is a perspective view showing a drum unit mounted in
a main casing of the laser printer;
[0034] FIG. 19 is a perspective view of the laser printer in FIG.
18 with a portion cut out;
[0035] FIG. 20 is a perspective view showing the drum unit
partially withdrawn from the main casing;
[0036] FIG. 21 is a perspective view showing the drum unit after
being removed from the main casing;
[0037] FIG. 22 is a perspective view from the left side of the drum
unit (with a rotatable nearside grip part);
[0038] FIG. 23 is a perspective view showing the drum unit mounted
in the main casing;
[0039] FIG. 24 is a perspective view showing the drum unit removed
from the main casing;
[0040] FIG. 25 is a perspective view from the bottom left side of
the drum unit provided with front feet and rear feet;
[0041] FIG. 26 is a left side view of the drum unit shown in FIG.
25;
[0042] FIG. 27A is a side view of a side plate illustrating the
positioning of drum shafts in the side plate according to a first
variation;
[0043] FIG. 27B is a enlarged view of FIG. 27A showing how the wire
spring urges the drum shaft;
[0044] FIG. 28 is an exploded perspective view of a drum subunit
according to a second variation;
[0045] FIG. 29 is a perspective view from the left side
illustrating the assembly of a pair of side plates to a front beam,
four drum subunits according to the second variation shown in FIG.
28, and a rear beam in a juxtaposed relationship;
[0046] FIG. 30 is a perspective view from the left side
illustrating the pair of side plates after being assembled to the
front beam, the four drum subunits shown in FIG. 28, and the rear
beam in a juxtaposed relationship;
[0047] FIG. 31 is a perspective view showing a drum unit mounted in
a main casing (with a rotatable near side grip part) of a printer
according to a sixth variation;
[0048] FIG. 32A is a side cross-sectional view of the printer
according to the sixth variation in a region including a front
cover and a handle to illustrate the movement of the front cover
toward a closed position and the rotation of the handle toward a
stored position, in which a protruding part of a guide on the front
cover is in contact with a distal end of the handle;
[0049] FIG. 32B is a side cross-sectional view of the printer
according to the sixth variation, in which a parallel part of the
guide is in contact with the distal end of the handle; and
[0050] FIG. 32C is a side cross-sectional view of the printer
according to the sixth variation, in which the front cover in the
closed position and the handle in the stored position.
DETAILED DESCRIPTION
[0051] A tandem photosensitive-member unit for an image-forming
device according to some aspects of the invention will be described
while referring to the accompanying drawings wherein like parts and
components are designated by the same reference numerals to avoid
duplicating description.
[0052] 1. General Structure of a Color Laser Printer
[0053] FIG. 1 is a side cross-sectional view showing a color laser
printer 1 as an aspect of the image-forming device of the
invention. FIG. 2 is a side cross-sectional view of a drum subunit
provided in the color laser printer 1 of FIG. 1 on which a
developer cartridge 22 is mounted. FIG. 3 is a side cross-sectional
view of the developer cartridge 22 shown in FIG. 2.
[0054] As shown in FIG. 1, a color laser printer 1 is a horizontal
tandem-type printer having a plurality of drum subunits 23
juxtaposed in a horizontal direction. The printer 1 includes a main
casing 2 and, within the main casing 2, a feeding unit 4 for
supplying sheets of a paper 3, an image-forming unit 5 for forming
images on the paper 3 supplied from the feeding unit 4, and a
discharge unit 6 for discharging the paper 3 after an image has
been formed thereon.
[0055] In the following description, the right side of the printer
1 in FIG. 1 (side of the main casing 2 in which a drum access
opening 162 is formed) will be referred to as the "front side,"
while the left side of the printer 1 in FIG. 1 will be referred to
as the "rear side." Further, the near side in FIG. 1 with respect
to the paper width direction will be referred to as the "left
side," while the far side in FIG. 1 will be referred to as the
"right side."
[0056] Unless otherwise stated below, directions in the following
description of a drum unit 21 and developer cartridges 22 will
conform to the state in which the drum unit 21 and developer
cartridges 22 are mounted in the main casing 2.
[0057] (1) Feeding Unit
[0058] The feeding unit 4 includes a paper tray 7 for accommodating
the paper 3 that can be slid into or removed from a
tray-accommodating section 171, described later, in a lower section
of the main casing 2 in a front-to-rear direction; a separating
roller 8 and a separating pad 9 disposed above a front end of the
paper tray 7 and in confrontation with each other; and a feeding
roller 10 disposed on the rear side of the separating roller 8.
[0059] The feeding unit 4 includes a feeding-end paper-conveying
path 11 for guiding the paper 3 conveyed from the paper tray 7. The
feeding-end paper-conveying path 11 is substantially U-shaped in a
side view for initially guiding the paper 3 forward and
subsequently reversing directions toward the rear. The feeding-end
paper-conveying path 11 has an upstream end positioned on the lower
side of the U-shape adjacent to the separating roller 8, and a
downstream end positioned on the upper side of the U-shape adjacent
to a conveying belt 53 described later.
[0060] The feeding unit 4 also includes a paper dust roller 12 and
a pinch roller 13 disposed in confrontation with each other along
the feeding-end paper-conveying path 11 and positioned above and
forward of the separating roller 8; and a pair of registration
rollers 14 also disposed on the feeding-end paper-conveying path 11
above the paper dust roller 12 and pinch roller 13.
[0061] A paper-pressing plate 15 is provided inside the paper tray
7 for supporting the paper 3 in a stacked state. The paper-pressing
plate 15 is pivotably supported on the rear end thereof, so that
the front end can pivot downward to a resting position in which the
paper-pressing plate 15 rests on a bottom plate of the paper tray 7
and can pivot upward to a feeding position in which the
paper-pressing plate slopes upward from the rear end to the front
end.
[0062] A lever 16 is provided in the lower front section of the
paper tray 7 for lifting the front end of the paper-pressing plate
15 upward. The lever 16 is pivotably supported at a position below
the front end of the paper-pressing plate 15 so that the front end
of the lever 16 can move up and down.
[0063] By pivoting the lever 16, the lever 16 lifts the front end
of the paper-pressing plate 15, shifting the paper-pressing plate
15 into the feeding position. When the paper-pressing plate 15 is
in the feeding position, the topmost sheet of paper 3 stacked on
the paper-pressing plate 15 is pressed against the feeding roller
10. When the feeding roller 10 rotates, the paper 3 is fed toward a
position between the separating roller 8 and separating pad 9.
[0064] When the paper tray 7 is removed from the main casing 2, the
paper-pressing plate 15 settles into the resting position. While
the paper-pressing plate 15 is in the resting position, sheets of
the paper 3 can be stacked on the paper-pressing plate 15. After
the feeding roller 10 has fed the paper 3 to a position between the
separating roller 8 and separating pad 9, the rotating separating
roller 8 separates and conveys the paper 3 one sheet at a time. The
sheet conveyed by the separating roller 8 passes between the paper
dust roller 12 and pinch roller 13, at which time the paper dust
roller 12 removes paper dust from the paper 3, and continues along
the feeding-end paper-conveying path 11 toward the registration
rollers 14.
[0065] After registering the paper 3, the registration rollers 14
convey the paper 3 to the conveying belt 53.
[0066] (2) Image-Forming Unit
[0067] (2-1) Scanning Unit
[0068] The image-forming unit 5 includes a scanning unit 17, a
process unit 18, a transfer unit 19, and a fixing unit 20. A single
scanning unit 17 is disposed in the top section of the main casing
2. Although not shown in the drawings, the scanning unit 17
includes a laser light-emitting unit, a polygon mirror, and a
plurality of lenses and reflecting mirrors. The laser
light-emitting unit emits laser beams based on image data for each
color. After passing through the lenses and reflecting off the
reflecting mirrors, the laser beams irradiate respective
photosensitive drums 24 corresponding to each color.
[0069] (2-2) Process Unit
[0070] The process unit 18 is disposed below the scanning unit 17
and above the feeding unit 4. As will be described later, the
process unit 18 includes a single drum unit 21, and four developer
cartridges 22 corresponding to the four colors.
[0071] (2-2-1) Drum Unit
[0072] As will be described in detail later, the drum unit 21 is
detachably mounted in a drum-accommodating section 161 of the main
casing 2 from the front side of the main casing 2 in a
front-to-rear direction. The drum unit 21 includes four drum
subunits 23 for each of the four colors. Specifically, the four
drum subunits 23 are a yellow drum subunit 23Y, a magenta drum
subunit 23M, a cyan drum subunit 23C, and a black drum subunit
23K.
[0073] The drum subunits 23 are disposed parallel to each other at
intervals in the front-to-rear direction. Specifically, the drum
subunits 23 are arranged from the front side to the rear side in
the order yellow drum subunit 23Y, magenta drum subunit 23M, cyan
drum subunit 23C, and black drum subunit 23K. As will be described
later, each drum subunit 23 includes a pair of side frame sections
71, and a center frame section 72 spanning between the side frame
sections 71 (see FIGS. 9 and 10).
[0074] As shown in FIG. 2, each drum subunit 23 holds the
photosensitive drum 24, a Scorotron charger 25, and a cleaning
brush 68.
[0075] The photosensitive drum 24 extends in a width direction
(hereinafter, the width direction will denote a left-to-right
direction orthogonal to the front-to-rear direction and the
vertical direction). The photosensitive drum 24 includes a main
drum body 26 that is cylindrical in shape and has a positive
charging photosensitive layer formed of polycarbonate on its outer
surface, and a drum shaft 27 disposed along the axis of the main
drum body 26.
[0076] Both widthwise ends of the drum shaft 27 are inserted into
the side frame sections 71 described later (see FIG. 10) and are
positioned by side plates 121 described later (see FIG. 7).
[0077] Rotational support members 30 (see FIG. 12A) are fitted onto
both axial ends of the main drum bodies 26 so as to be incapable of
rotating relative to the same but capable of rotating relative to
the drum shafts 27. With this structure, the main drum bodies 26
are rotatably supported on the drum shafts 27. During an
image-forming process, the photosensitive drum 24 is rotated by a
driving force transmitted from a motor (not shown) provided in the
main casing 2.
[0078] As shown in FIG. 2, the charger 25 is supported on the
center frame section 72 described later diagonally above and
rearward of the photosensitive drum 24. The charger 25 opposes the
photosensitive drum 24 at a distance. The charger 25 includes a
discharge wire 28 disposed in opposition to but separated from the
photosensitive drum 24, and a grid 29 provided between the
discharge wire 28 and photosensitive drum 24.
[0079] The discharge wire 28 is connected to a wire electrode 80
(see FIG. 12B) described later. The grid 29 is connected to a grid
electrode 81 (FIG. 12B) described later.
[0080] During an image-forming operation, a high-voltage circuit
board (not shown) provided in the main casing 2 applies a high
voltage to the discharge wire 28 via the wire electrode 80 to
produce a corona discharge from the discharge wire 28. At the same
time, a high-voltage circuit board (not shown) provided in the main
casing 2 applies a high voltage to the grid via the grid electrode
81 to apply a uniform positive charge to the surface of the
photosensitive drum 24 while controlling the amount of charge
supplied thereto.
[0081] The cleaning brush 68 is supported on the center frame
section 72 described later at a position rearward of the
photosensitive drum 24 and opposes and is in contact with the
photosensitive drum 24. During an image-forming operation, the
high-voltage circuit board (not shown) provided in the main casing
2 applies a cleaning bias to the cleaning brush 68 via a cleaning
electrode 83 described later (see FIG. 12B).
[0082] (2-2-2) Developer Cartridge
[0083] As shown in FIG. 1, the developer cartridges 22 are
detachably mounted in correspondence to the drum subunits 23 for
each color. Specifically, the developer cartridges 22 include a
yellow developer cartridge 22Y detachably mounted on the yellow
drum subunit 23Y, a magenta developer cartridge 22M detachably
mounted on the magenta drum subunit 23M, a cyan developer cartridge
22C detachably mounted on the cyan drum subunit 23C, and a black
developer cartridge 22K detachably mounted on the black drum
subunit 23K.
[0084] As shown in FIG. 3, each developer cartridge 22 includes a
developer frame 31 and, within the developer frame 31, an agitator
32, a supply roller 33, a developing roller 34, and a
thickness-regulating blade 35.
[0085] The developer frame 31 is formed in a box shape having an
opening 36 on the lower end. A partitioning wall 39 is provided
midway in the developer frame 31 with respect to the vertical for
partitioning the interior of the developer frame 31 into a
toner-accommodating chamber 37 and a developing chamber 38. A
through-hole 40 is formed in the partitioning wall 39 to allow
communication between the toner-accommodating chamber 37 and
developing chamber 38.
[0086] The toner-accommodating chamber 37 accommodates toner
corresponding to one of the four colors. More specifically, the
toner-accommodating chamber 37 of the yellow developer cartridge
22Y accommodates yellow toner, the toner-accommodating chamber 37
of the magenta developer cartridge 22M accommodates magenta toner,
the toner-accommodating chamber 37 of the cyan developer cartridge
22C accommodates cyan toner, and the toner-accommodating chamber 37
of the black developer cartridge 22K accommodates black toner.
[0087] The toner of each color is a nonmagnetic, single-component
toner having a positive charge. The polymerized toner is spherical
in shape and is obtained by co-polymerizing a polymerized monomer
using a well-known polymerization method such as suspension
polymerization. The polymerized monomer may be, for example, a
styrene monomer such as styrene or an acrylic monomer such as
acrylic acid, alkyl (C1-C4) acrylate, or alkyl (C1-C4) meta
acrylate. The base particle of the toner is formed primarily of a
binding resin that is compounded with a coloring agent of the
corresponding color, a charge-controlling agent, wax, and the like
and further includes an additive for improving fluidity.
[0088] A coloring agent in yellow, magenta, cyan, and black is
compounded to produce each of these colors. The charge-controlling
agent is a charge-controlling resin obtained by co-polymerizing an
ionic monomer having an ionic functional group, such as ammonium
salt, with a monomer that can be co-polymerized with an ionic
monomer, such as a styrene monomer or an acrylic monomer. The
additive may be powder of a metal oxide, such as silica, aluminum
oxide, titanium oxide, strontium titanate, cerium oxide, or
magnesium oxide; or an inorganic powder, such as a carbide powder
or metal salt powder.
[0089] Windows 142 are also formed in the toner-accommodating
chamber 37 for detecting the amount of toner remaining in the
toner-accommodating chamber 37. The windows 142 are embedded in
both side walls 141 of the developer frame 31 at positions opposing
each other across the toner-accommodating chamber 37 (FIG. 8).
[0090] The agitator 32 is disposed in the toner-accommodating
chamber 37 and includes a rotational shaft 41 rotatably supported
in both side walls 141 of the developer frame 31, and an agitating
member 42 provided on the rotational shaft 41 along the axial
direction thereof and extending radially outward from the
rotational shaft. During image formation, a driving force from a
motor (not shown) provided in the main casing 2 is transmitted to
the rotational shaft 41 via a passive coupling gear 144 (see FIG.
17), causing the agitating member 42 to move circularly within the
toner-accommodating chamber 37.
[0091] The supply roller 33 is disposed inside the developing
chamber 38 below the through-hole 40. The supply roller 33 includes
a supply roller shaft 43 formed of metal that is rotatably
supported in both side walls 141 of the developer frame 31, and a
sponge roller 44 formed of an electrically conductive sponge
material covering the periphery of the supply roller shaft 43.
During image formation, a driving force from a motor (not shown)
provided in the main casing 2 is transmitted to the supply roller
shaft 43 via the passive coupling gear 144 to drive the supply
roller 33 to rotate.
[0092] The developing roller 34 is disposed inside the developing
chamber 38 diagonally below and rearward of the supply roller 33.
The developing roller 34 includes a developing roller shaft 45
formed of metal and rotatably supported in both side walls 141 of
the developer frame 31, and a rubber roller 46 formed of an
electrically conductive rubber that covers the periphery of the
developing roller shaft 45.
[0093] More specifically, the rubber roller 46 has a two layer
structure including a rubber roller layer configured of an
electrically conductive urethane rubber, silicon rubber, EPDM
rubber, or the like containing fine carbon particles and the like;
and a coating applied to the surface of the rubber roller layer and
formed primarily of urethane rubber, urethane resin, polyimide
resin, or the like. A developing roller electrode 82 described
later (see FIG. 12B) is connected to the developing roller shaft
45.
[0094] The developing roller 34 is disposed against the supply
roller 33 so as to generate pressure between the rubber roller 46
and sponge roller 44. The developing roller 34 is also exposed on
the bottom of the developer cartridge 22 through the opening
36.
[0095] During image formation, a driving force from a motor (not
shown) provided in the main casing 2 is transmitted to the
developing roller shaft 45 via the passive coupling gear 144 (FIG.
17) for rotating the developing roller 34. A developing bias
supplied from the high-voltage circuit board (not shown) provided
in the main casing 2 is also applied to the developing roller 34
via the developing roller electrode 82.
[0096] The thickness-regulating blade 35 is disposed in the
developing chamber 38 so as to press against the developing roller
34 from above. The thickness-regulating blade 35 includes a blade
48 configured of a metal leaf spring member, and a pressing part 49
provided on a distal end of the blade 48. The pressing part 49 is
formed of an insulating silicon rubber and has a semicircular
cross-section.
[0097] A base end of the blade 48 is fixed to the partitioning wall
39 by a fixing member 47, while the elastic force of the blade 48
causes the pressing part 49 on the distal end to contact the rubber
roller 46 of the developing roller 34 from above.
[0098] (2-2-3) Developing Operation in the Process Unit
[0099] In each developer cartridge 22, toner of the corresponding
color accommodated in the toner-accommodating chamber 37 shifts
toward the through-hole 40 by its own weight. As the agitator 32
agitates the toner, some of the toner is discharged through the
through-hole 40 into the developing chamber 38.
[0100] Toner discharged through the through-hole 40 into the
developing chamber 38 is supplied onto the supply roller 33. As the
supply roller 33 rotates, the toner borne on the supply roller 33
is supplied to the developing roller 34. At this time, the toner is
positively tribocharged between the supply roller 33 and the
developing roller 34 as a developing bias is applied to the
developing roller 34.
[0101] As the developing roller 34 rotates, toner supplied to the
surface of the developing roller 34 passes between the pressing
part 49 of the thickness-regulating blade 35 and the rubber roller
46 of the developing roller 34, thereby maintaining a thin layer of
uniform thickness on the surface of the rubber roller 46.
[0102] In the meantime, as shown in FIG. 2, the charger 25 in the
drum subunit 23 corresponding to the developer cartridge 22
generates a corona discharge for charging the surface of the
photosensitive drum 24 with a uniform positive polarity. As the
photosensitive drum 24 continues to rotate, a laser beam emitted
from the scanning unit 17 is scanned at a high speed over the
positively charged surface of the photosensitive drum 24, forming
an electrostatic latent image on the photosensitive drum 24
corresponding to an image that will be formed on the paper 3.
[0103] Next, positively charged toner borne on the surface of the
developing roller 34 comes into contact with the photosensitive
drum 24 as the developing roller 34 rotates and is supplied to
areas on the surface of the positively charged photosensitive drum
24 that were exposed to the laser beam and, therefore, have a lower
potential. In this way, the latent image on the photosensitive drum
24 is developed into a visible image according to a reverse
development process so that the photosensitive drum 24 bears a
toner image corresponding to the relevant color.
[0104] Toner remaining on the photosensitive drum 24 after the
transfer operation is recovered by the developing roller 34.
Further, paper dust deposited on the photosensitive drum 24 from
the paper 3 is removed by the cleaning brush 68.
[0105] (2-3) Transfer Unit
[0106] As shown in FIG. 1, the transfer unit 19 is disposed in the
main casing 2 above the feeding unit 4 and extends in the
front-to-rear direction beneath the process unit 18. The transfer
unit 19 includes a drive roller 51, a follow roller 52, the
conveying belt 53, transfer rollers 54, and a cleaning unit 55.
[0107] The drive roller 51 and follow roller 52 are disposed in
opposition to each other across a distance in the front-to-rear
direction. The drive roller 51 is disposed rearward of the black
drum subunit 23K, while the follow roller 52 is disposed forward of
the yellow drum subunit 23Y.
[0108] The conveying belt 53 is an endless belt formed of a
synthetic resin film such as an electrically conductive
polycarbonate or polyimide containing dispersed conductive
particles such as carbon. The conveying belt 53 is looped around
the drive roller 51 and follow roller 52.
[0109] During image formation, a driving force from a motor (not
shown) provided in the main casing 2 is transferred to the drive
roller 51 for rotating the same. When the drive roller 51 is driven
to rotate, the conveying belt 53 travels in a circuit around the
drive roller 51 and follow roller 52, while the follow roller 52
follows the movement of the conveying belt 53. The conveying belt
53 moves in the same direction as the surfaces of the
photosensitive drums 24 at transfer positions in which the
conveying belt 53 contacts the photosensitive drums 24 of the drum
subunits 23.
[0110] The transfer rollers 54 are disposed inside the conveying
belt 53 at positions opposing each photosensitive drum 24 with the
conveying belt 53 interposed therebetween. The transfer rollers 54
are configured of a metal roller shaft covered with a rubber roller
that is formed of an electrically conductive rubber. The transfer
rollers 54 are rotatably provided so that the surfaces of the
transfer rollers 54 move in the same direction as the conveying
belt 53 at the transfer positions. During image formation, the
high-voltage circuit board (not shown) provided in the main casing
2 applies a transfer bias to the transfer rollers 54.
[0111] The cleaning unit 55 is disposed below the conveying belt 53
and includes a primary cleaning roller 56, a secondary cleaning
roller 57, a scraping blade 58, and a toner collector 59.
[0112] The primary cleaning roller 56 is disposed so as to contact
the lower portion of the conveying belt 53 on the side opposite the
upper portion of the conveying belt 53 that contacts the
photosensitive drums 24 and transfer rollers 54. The primary
cleaning roller 56 is configured to rotate in a direction that
follows the circular movement of the conveying belt 53. During
image formation, the high-voltage circuit board (not shown)
provided in the main casing 2 applies a primary cleaning bias to
the primary cleaning roller 56.
[0113] The secondary cleaning roller 57 is disposed below the
primary cleaning roller 56 and in contact with the same and is
configured to rotate so that the peripheral surface of the
secondary cleaning roller 57 moves in the same direction as the
primary cleaning roller 56 at the contact position. During image
formation, the high-voltage circuit board (not shown) provided in
the main casing 2 applies a secondary cleaning bias to the
secondary cleaning roller 57.
[0114] The scraping blade 58 is disposed in contact with the
secondary cleaning roller 57 from below.
[0115] The toner collector 59 is disposed below the primary
cleaning roller 56 and secondary cleaning roller 57 for collecting
toner that falls from the secondary cleaning roller 57.
[0116] The conveying belt 53 moving circuitously along the driving
of the drive roller 51 and the following of the follow roller 52
conveys the paper 3 supplied from the feeding unit 4 toward the
rear of the printer 1 so that the paper 3 sequentially passes
transfer positions corresponding to each drum subunit 23. As the
paper 3 is conveyed, toner images in each color borne on the
photosensitive drums 24 of each drum subunit 23 are sequentially
transferred onto the paper 3, forming a color image thereon.
[0117] For example, first the yellow toner image borne on the
surface of the photosensitive drum 24 in the yellow drum subunit
23Y is transferred onto the paper 3 after which the magenta toner
image borne on the surface of the photosensitive drum 24 in the
magenta drum subunit 23M is transferred onto the paper 3 and
superimposed over the yellow toner image already transferred. In
the same way, the cyan toner image and black toner image borne on
the surfaces of the photosensitive drums 24 in the cyan drum
subunit 23C and black drum subunit 23K, respectively, are
superimposed over the previously transferred toner images to form a
color image on the paper 3.
[0118] Any toner deposited on the surface of the conveying belt 53
in the transfer operation described above is subsequently cleaned
by the cleaning unit 55. First, the toner on the surface of the
conveying belt 53 is transferred to the primary cleaning roller 56
by a primary cleaning bias and is subsequently transferred to the
secondary cleaning roller 57 by a secondary cleaning bias. Next,
the scraping blade 58 scrapes off toner that has been transferred
onto the secondary cleaning roller 57. Toner scraped off the
secondary cleaning roller 57 drops into the toner collector 59.
[0119] (2-4) Fixing Unit
[0120] The fixing unit 20 is disposed in the main casing 2,
rearward of the black drum subunit 23K and opposite the transfer
position in which the photosensitive drum 24 contacts the conveying
belt 53 in the front-to-rear direction. The fixing unit 20 includes
a heating roller 61 and a pressure roller 62.
[0121] The heating roller 61 is configured of a metal tube, the
surface of which has been coated with a release layer. The metal
tube accommodates a halogen lamp extending along the axial
direction of the main casing 2 for heating the surface of the
heating roller 61 to a fixing temperature.
[0122] The pressure roller 62 is disposed below and in
confrontation with the heating roller 61. The pressure roller 62
presses against the heating roller 61 from the bottom thereof.
[0123] After a color image has been transferred onto a sheet of
paper 3, the paper 3 is conveyed to the fixing unit 20. In the
fixing unit 20, the color image is fixed to the paper 3 by heat as
the paper 3 passes between the heating roller 61 and pressure
roller 62.
[0124] (3) Discharge Unit
[0125] A discharge-end conveying path 63 is provided in the
discharge unit 6. The discharge-end conveying path 63 is
substantially U-shaped in a side view, with an upstream end
positioned on the lower side adjacent to the fixing unit 20 and a
downstream end positioned on the upper side adjacent to a discharge
tray 64 formed on top of the main casing 2. Hence, the
discharge-end conveying path 63 initially guides the paper 3
rearward, then reverses directions and discharges the paper 3 in a
forward direction.
[0126] A transfer roller 65 and a pinch roller 66 are disposed in
confrontation with each other along the discharge-end conveying
path 63. Further, a pair of discharge rollers 67 is disposed on the
downstream end of the discharge-end conveying path 63. The
discharge tray 64 is formed on top of the main casing 2 as a
depression that grows gradually deeper toward the rear side. The
discharge tray 64 functions to support sheets of discharged paper 3
in a stacked state.
[0127] After the paper 3 passes through the fixing unit 20, the
transfer roller 65 and pinch roller 66 convey the paper 3 along the
discharge-end conveying path 63 toward the discharge rollers 67 and
the discharge rollers 67 discharge the paper 3 onto the discharge
tray 64.
[0128] 2. Drum Unit
[0129] FIG. 4 is a perspective view from the left side of the drum
unit 21 in which the developer cartridges 22 are mounted. FIG. 5 is
a perspective view from the left side of the drum unit 21 in which
one of the developer cartridges 22 has been removed. FIG. 6 is a
plan view of the drum unit 21 shown in FIG. 4. FIG. 7 is a left
side view of the drum unit 21 shown in FIG. 4. FIG. 8 is a
cross-sectional view along a line VIII-VIII indicated in FIG. 7.
FIG. 9 is an exploded perspective view of the drum subunit 21. FIG.
10 is a perspective view of the drum subunit 21. FIG. 11 is a
perspective view from the left side illustrating the assembly of
the pair of side plates 121 to a front beam 96, four drum subunits
23, and a rear beam 111 in a juxtaposed relationship. FIG. 12A is a
perspective view from the right side illustrating the assembly of
the pair of side plates 121 to the front beam 96, four drum
subunits 23, and rear beam 111 in a juxtaposed relationship. FIG.
12B is an enlarged view of FIG. 12A illustrating electrodes. FIG.
13A is a side view illustrating the positioning of drum shafts 27
in the side plate 121. FIG. 13B is an enlarged view of FIG. 13A
illustrating portions near a wire spring 127. FIG. 13C is an
explanatory diagram showing how the wire spring 127 urges the drum
shaft 27. FIG. 14 is a perspective view from the left side
illustrating the pair of side plates 121 that have been assembled
to the front beam 96, four drum subunits 23, and the rear beam 111
in a juxtaposed relationship. FIG. 15A is a perspective view from
the right side illustrating the pair of side plates 121 that have
been assembled to the front beam 96, four drum subunits 23, and
rear beam 111 in a juxtaposed relationship. FIG. 15B is an enlarged
view of FIG. 15A illustrating electrodes.
[0130] Next, the drum unit 21 will be described with reference to
FIGS. 4 through 15B.
[0131] As shown in FIG. 4, the drum unit 21 includes the four drum
subunits 23 corresponding to the four colors and juxtaposed in the
front-to-rear direction; the front beam 96 and the rear beam 111
disposed on front and rear sides of the four drum subunits 23; and
the pair of side plates 121 disposed on widthwise ends of the front
beam 96, the four drum subunits 23, and the rear beam 111. The four
drum subunits 23 (frame construction except for the photosensitive
drums 24 and the like), the front beam 96, the rear beam 111, and
the pair of side plates 121 constitute a unit frame.
[0132] The four drum subunits 23, the front beam 96, the rear beam
111, and the pair of side plates 121 constituting the drum unit 21
can be slidably mounted into or removed from the drum access
opening 162 of the main casing 2 as an integrated unit.
[0133] (1) Drum Subunits
[0134] As shown in FIGS. 9 and 10, the drum subunit 23 includes the
pair of side frame sections 71 disposed in opposition to each other
over a distance in the width direction, and the center frame
section 72 that spans between the side frame sections 71.
[0135] (1-1) Side Frame Sections
[0136] Each of the side frame sections 71 is formed of a synthetic
resin material and has a substantially rectangular plate shape in a
side view. More specifically, the side frame sections 71 are shaped
substantially like parallelograms in a side view and slope downward
and to the rear.
[0137] Guide grooves 73 are formed in the inner wall surfaces of
the side frame sections 71 at positions opposing each other in the
width direction for guiding the developer cartridge 22 as the
developer cartridge 22 is mounted in or removed from the drum
subunit 23.
[0138] The guide grooves 73 in the inner wall surfaces of the side
frame sections 71 are formed substantially in a vertical direction
from the top edge near the rear side of the side frame section 71
to a point near the lower edge on the front side of the side frame
section 71. The upstream ends of the guide grooves 73 are wider and
open toward the top. The downstream ends of the guide grooves 73
(deepest parts) are disposed at positions corresponding to the
developing roller shafts 45 when the developer cartridge 22 is
mounted on the drum subunit 23 so that the developing roller 34
contacts the photosensitive drum 24. The guide grooves 73 are
formed as depressions in the inner wall surfaces of the side frame
section 71 depressed outward in the width direction. As shown in
FIG. 16, electrically conductive collar members 50 are slidably
received in the guide grooves 73 for covering both widthwise ends
of the developing roller shaft 45.
[0139] As shown in FIG. 9, bosses 75 are formed in the upper side
of the side frame sections 71 at positions forward of the guide
grooves 73. The bosses 75 are cylindrical in shape and have a
hollow that penetrates the side frame section 71. The bosses 75
protrude outward in the width direction from the outer wall of the
side frame sections 71. When the developer cartridge 22 is mounted
on the drum subunit 23, the windows 142 (see also FIG. 17) of the
developer cartridge 22 oppose each other in the width direction
through the bosses 75, as shown in FIG. 8.
[0140] Drum support units 76 (FIG. 9) are formed in the side frame
sections 71 for supporting the photosensitive drum 24. Each drum
support unit 76 includes a receiving part 77 formed in the inner
wall surface of the side frame section 71 on the lower end of the
same and having a cylindrical shape that is depressed outward in
the width direction. The receiving part 77 receives a cylindrical
axial insertion part 90 of the center frame section 72 described
next. Axial insertion through-holes 78 are formed in the center of
the receiving parts 77 and penetrate the side frame sections 71 in
the thickness direction.
[0141] Two threaded through-holes 79 are formed in each side frame
section 71 on the rear edge thereof, penetrating the side frame
sections 71 in the thickness direction. Screws 92 are inserted into
the threaded through-holes 79 for fixing the side frame sections 71
to the center frame section 72. One of the threaded through-holes
79 is formed in the lower rear edge of the side frame section 71,
while the other is formed midway along the rear edge.
[0142] Protruding ridges 84 extending in the front-to-rear
direction are formed on each side frame section 71 above the boss
75. The protruding ridges 84 are formed as narrow seams extending
in the front-to-rear direction and protruding outward in the width
direction from the outer wall surface of the side frame sections
71.
[0143] As shown in FIG. 9, a coupling inner through-hole 74 is
formed in the side frame section 71 on the left side midway in the
guide groove 73 at a position corresponding to the passive coupling
gear 144 (FIG. 17) of the developer cartridge 22 in the width
direction when the developer cartridge 22 is mounted on the drum
subunit 23. The coupling inner through-hole 74 is a circular hole
penetrating the left side frame section 71 in the width
direction.
[0144] A screw receiving part 85 is also provided in the left side
frame section 71 between the coupling inner through-hole 74 and
axial insertion through-hole 78. A screw 136 (see FIG. 11) is
screwed into the screw receiving part 85 to fasten the side plate
121 to the drum subunit 23. The screw receiving part 85 is
cylindrical in shape and protrudes outward in the width direction
from the outer wall surface of the side frame section 71.
[0145] As shown in FIG. 12B, the wire electrodes 80, grid
electrodes 81, developing roller electrodes 82, and cleaning
electrodes 83 are supported in the right side frame section 71 by
being inserted through the side frame section 71 in the thickness
direction so as to protrude outward in the width direction from the
outer wall surface of the side frame section 71.
[0146] The wire electrodes 80 are disposed above the axial
insertion through-holes 78 in substantially the vertical center and
front-to-rear center of the side frame section 71.
[0147] The grid electrodes 81 are disposed diagonally above and
rearward of the axial insertion through-holes 78 on the rear edge
of the side frame sections 71 and in substantially the vertical
middle thereof.
[0148] The developing roller electrodes 82 are disposed diagonally
above and forward of the axial insertion through-holes 78 near the
front edge of the side frame sections 71 and in the vertical middle
thereof.
[0149] The cleaning electrodes 83 are disposed diagonally above and
rearward of the axial insertion through-holes 78, above the grid
electrodes 81, and near the rear edges of the side frame sections
71 in the vertical middle thereof.
[0150] Further, peripheral fitting walls 94 are provided at
positions corresponding to each of the wire electrodes 80. Each
fitting wall 94 protrudes outward in the width direction from the
outer wall surface of the right side frame section 71 and forms a
semicircular arc around the wire electrode 80.
[0151] (1-2) Center Frame Section
[0152] As shown in FIGS. 9 and 10, the center frame section 72 is
molded from a synthetic resin material independently of the side
frame sections 71. The center frame section 72 is integrally
configured of a center plate 86 extending in the width direction,
and side inner plates 87 disposed on both widthwise ends of the
center plate 86.
[0153] A charger holding unit 88 having a substantially narrow
plate shape in a plan view is provided in the vertical center of
the center plate 86 extending in the width direction for holding
the charger 25. The charger holding unit 88 holds the discharge
wire 28 extending in the width direction, and the grid 29 below the
discharge wire 28 (see FIG. 2). The charger holding unit 88 also
holds a wire cleaner 89 that grips the discharge wire 28 and is
capable of sliding over the discharge wire 28 in the width
direction.
[0154] The center plate 86 is also provided with a brush holding
unit 93 disposed below the charger holding unit 88 for holding the
cleaning brush 68. The cleaning brush 68 held by the brush holding
unit 93 spans the brush holding unit 93 in the width direction (see
FIG. 2).
[0155] The inner plates 87 provided on the widthwise ends of the
center plate 86 are formed by bending the center plate 86 in a
forward direction. In a side view, each inner plate 87 has a
substantially triangular shape that narrows toward the front. The
cylindrical axial insertion part 90 is provided in this front end
of the inner plate 87 for receiving the drum shaft 27.
[0156] Further, screw receiving parts 91 are formed in both upper
and lower ends of each inner plate 87 on the rear edge thereof and
extend from the outer wall surface of the inner plate 87 inward in
the width direction along the center plate 86. The screws 92 are
screwed into the screw receiving parts 91 to mount the side frame
section 71 on the center frame section 72.
[0157] (1-3) Assembly of the Drum Subunit
[0158] As shown in FIG. 9, the side frame sections 71 are
positioned on both widthwise ends of the center frame section 72.
The center frame section 72 is interposed between the side frame
sections 71 in the following way. First, the cylindrical axial
insertion parts 90 of the center frame section 72 are inserted into
the receiving parts 77 in the drum support units 76 of the side
frame sections 71 in order to overlap the axial insertion
through-holes 78 in the width direction. Simultaneously, the screw
receiving parts 91 of the center frame section 72 overlaps the
threaded through-holes 79 of the side frame sections 71 in the
width direction. Next, the screws 92 are inserted through the
threaded through-holes 79 and screwed into the screw receiving
parts 91. As a result, the side frame sections 71 are mounted on
both widthwise ends of the center frame section 72, as shown in
FIG. 10, completing assembly of the drum subunit 23.
[0159] When the side frame sections 71 are mounted on both ends of
the center frame section 72, the center plate 86 of the center
frame section 72 contacts the side frame sections 71 in a region on
the rear edge from the bottom end to a vertical midpoint and spans
between both side frame sections 71.
[0160] When the side frame sections 71 are mounted on both
widthwise ends of the center frame section 72, the wire electrode
80 and grid electrode 81 provided on the right side frame section
71 form a connection with the discharge wire 28 and grid 29 on the
center frame section 72. Further, the cleaning electrode 83 is
connected to the cleaning brush 68.
[0161] Further, the photosensitive drum 24 is retained in the drum
subunit 23. Specifically, the main drum body 26 fitted into the
rotational support members 30 (see FIG. 12A) and incapable of
rotating relative to the same is disposed between the inner plates
87 so as to be parallel to but separated a distance from the
charger 25. Next, the drum shaft 27 is inserted through the axial
insertion through-holes 78 of the side frame section 71 and the
cylindrical axial insertion parts 90 of the center frame section 72
along the axis of the main drum body 26 and is fixed so as to be
incapable of rotating relative to the axial insertion through-holes
78. The drum shafts 27 rotatably support the rotational support
members 30 supporting the main drum body 26, thereby retaining the
photosensitive drum 24 in the drum subunit 23.
[0162] By supporting both axial ends of the drum shaft 27, the side
frame sections 71 can be positioned relative to each other via the
drum shaft 27.
[0163] (2) Front Beam
[0164] As shown in FIGS. 11 and 12A, the front beam 96 is disposed
in front of the four drum subunits 23 juxtaposed in the
front-to-rear direction and spans between the pair of side plates
121.
[0165] The front beam 96 includes a pair of side walls 97 opposing
each other in the width direction, and a front wall 98 and a rear
wall 99 spanning between the pair of side walls 97. The components
of the front beam 96 are integrally molded from a synthetic resin
material.
[0166] Each side wall 97 includes a side wall base part 100
substantially shaped like a parallelogram in a side view, and a
side wall leg part 101 that extends diagonally downward and
rearward from the lower end of the side wall base part 100. A front
screw receiving part 103 is provided on the outer wall surface of
the side wall base part 100. A screw 136 is screwed into the front
screw receiving part 103 for attaching the side plate 121.
[0167] Front sloped surfaces 102 sloping downward to the rear are
formed on rear endfaces of the side wall 97 linking the side wall
base part 100 to the side wall leg part 101.
[0168] The front wall 98 has a substantially narrow rectangular
shape in a front view and extends in the width direction The front
wall 98 is vertically oriented and extends between the pair of side
walls 97.
[0169] A near side grip part (front side grip part) 104 is provided
in the widthwise center of the front wall 98. The near side grip
part 104 is configured of a pair of side plates 105 disposed in
opposition to each other across a distance in the width direction,
and a center plate 106 spanning between the side plates 105.
[0170] Each side plate 105 is formed substantially in a triangular
plate shape when viewed from the side and protrudes forward from
the front wall surface of the front wall 98. The front edge of the
side plate 105 slopes diagonally forward and downward.
[0171] The center plate 106 spans between the lower edge portions
of the side plates 105 and has a L-shaped cross-section that
extends outward from the front wall surface of the front wall 98
and bends upward.
[0172] The near side grip part 104 is positioned so that the
widthwise center matches the widthwise center of the front beam 96.
Hence, after assembling the drum unit 21, the widthwise center of
the near side grip part 104 is aligned with a straight line X1
passing through the widthwise center of the drum subunit 23 in the
front-to-rear direction, as shown in FIG. 6.
[0173] As shown in FIG. 11, the rear wall 99 has an elongated
rectangular plate shape in a rear view that extends in the width
direction. The rear wall 99 is disposed to the rear of the front
wall 98 and spans between the side walls 97 while sloping downward
and rearward along the front sloped surface 102 of the side walls
97.
[0174] (3) Rear Beam
[0175] As shown in FIGS. 11 and 12A, the rear beam 111 is disposed
on the rear side of the four drum subunits 23 juxtaposed in the
front-to-rear direction and spans between the pair of side plates
121.
[0176] The rear beam 111 is integrally molded of a synthetic resin
material and includes a pair of side walls 112 opposing each other
in the width direction, and a bridging wall 113 spanning between
the pair of side walls 112.
[0177] The side wall 112 has a substantially triangular plate shape
in a side view that narrows toward the bottom. A screw receiving
part 114 is provided in the outer wall surface of the side wall 112
for attaching the side plate 121 with a screw 136. A rear sloping
surface 115 sloping downward and to the rear is formed on the front
endface of the side wall 112.
[0178] The bridging wall 113 has a substantially elongated
rectangular plate shape in a rear view and extends in the width
direction. The bridging wall 113 is erected vertically and spans
between the pair of side walls 112.
[0179] The front wall surface of the bridging wall 113 is a flat
surface that slopes downward and rearward along the rear sloping
surfaces 115 of the side walls 112.
[0180] A far side grip part (rear side grip part) 116 is disposed
in the widthwise center of the bridging wall 113. The far side grip
part 116 includes a depressed part 117 formed by depressing the top
edge of the bridging wall 113 downward in a rear view, and a rear
grip 118 forming three sides of a rectangle in a rear view and
linked with the top edge of the bridging wall 113.
[0181] A ventilation hole 119 having a substantially elongated
rectangular shape in a rear view is formed between the depressed
part 117 and rear grip 118 to allow the passage of air in an air
flow direction (front-to-rear direction), as will be described
later.
[0182] The far side grip part 116 is positioned so that the
widthwise center matches the widthwise center of the rear beam 111.
Hence, after assembling the drum unit 21, the widthwise center of
the far side grip part 116 is positioned on the straight line X1
that passes through the widthwise center of the drum subunit 23 in
the front-to-rear direction, as shown in FIG. 6.
[0183] (4) Side Plates
[0184] As shown in FIGS. 11 and 12A, a pair of the side plates 121
is provided so as to be able to sandwich the front beam 96, the
four drum subunits 23, and the rear beam 111 from both widthwise
edges thereof.
[0185] The side plate 121 is formed of a material having a lower
linear coefficient of expansion than that of the synthetic resin
material used to form the drum subunits 23. For example, the side
plates 121 are formed of metal or fiber reinforced resin, and
preferably metal.
[0186] Each side plate 121 has a substantially elongated
rectangular plate shape in a side view that extends in the
front-to-rear direction. When assembling the drum unit 21, as will
be described later, the side plates 121 are formed to oppose the
front beam 96, drum subunits 23, and rear beam 111 juxtaposed in
the front-to-rear direction so that the front edge opposes the
front beam 96 and the rear edge opposes the rear beam 111. The side
plates 121 are also formed so that the top edge opposes the
protruding ridges 84 of the side frame sections 71 and the bottom
edge opposes the lower edge of the side frame sections 71.
[0187] A flange part 122 serving as a fitting part is formed across
the top edge of each side plate 121 in the front-to-rear direction
and extends outward in the width direction. The flange part 122 is
formed by bending the top edge of the side plate 121 outward in the
width direction to form a L-shaped cross-section. The flange part
122 can be slidably fit in a rail 164 (see FIG. 20) of the
drum-accommodating section 161 described later, serving as a guide
part.
[0188] Four light transmitting through-holes 123 are formed in the
top edge of each side plate 121 for receiving the boss 75 of each
drum subunit 23 when the side frame sections 71 are mounted on the
drum subunit 23.
[0189] The four light transmitting through-holes 123 are formed in
the top edge of the side plate 121 at intervals in the
front-to-rear direction. The light transmitting through-holes 123
are formed as circular through-holes penetrating the side plate 121
in the thickness direction at positions aligned with the window 142
(FIG. 17) of the developer cartridge 22 and the bosses 75 in the
width direction when the side frame sections 71 are mounted on the
drum subunits 23 and the developer cartridges 22 are mounted on the
drum subunits 23, as shown in FIG. 17.
[0190] As shown in FIG. 12A, four shaft through-holes 124 are
formed along the lower edge of each side plate 121 for receiving
the axial ends of each drum shaft 27 when the side frame sections
71 are mounted on the drum subunit 23.
[0191] Four of the shaft through-holes 124 are formed in the lower
edge of the side plate 121 at intervals along the front-to-rear
direction. The shaft through-holes 124 are square holes that
penetrate the side plate 121 in the thickness direction at
positions opposing the axial ends of the drum shafts 27 in the
width direction when the side frame sections 71 are mounted on the
drum subunit 23. More specifically, each shaft through-hole 124 is
substantially rectangular in shape in a side view with sides
parallel to the front-to-rear direction and the vertical direction,
as shown in FIG. 13A. The top and front peripheral edges of the
shaft through-hole 124 form two straight lines that intersect each
other at approximately a right angle. These peripheral edges form
contact surfaces 131 described later that are contacted by the drum
shaft 27 at points.
[0192] A pair of engaging holes 126 are formed in each side plate
121 corresponding to each shaft through-hole 124 at positions
slightly above and on either side in the front-to-rear direction of
the shaft through-hole 124. One of the engaging holes 126 formed in
the right side plate 121 is formed continuously with a center
opening 133 described later.
[0193] As shown in FIGS. 13A, 13B, and 13C, at the inner wall
surface of the right side plate 121, the wire spring 127 is engaged
in the pair of engaging holes 126 for axial positioning. The wire
spring 127 is configured of a substantially V-shaped wire in a side
view, with both upper ends bent outward in the width direction.
[0194] Each wire spring 127 is arranged along the inner wall
surface of the side plate 121 with the upper ends engaged in the
pair of engaging holes 126. Hence, the wire spring 127 is retained
on the side plate 121 between the pair of engaging holes 126 such
that the center region is depressed downward in a V-shape when
viewed from the side. Further, the wire spring 127 is positioned
such that the rear side crosses diagonally through the shaft
through-hole 124 upward and rearward.
[0195] As shown in FIGS. 11 and 12A, a front screw through-hole 128
is formed near the front edge of each side plate 121 at a position
opposing the front screw receiving part 103 of the side wall base
part 100 when the side plates 121 are mounted on the front beam 96.
A screw 136 is inserted through the front screw through-hole
128.
[0196] Further, a rear screw through-hole 129 is formed near the
rear edge of each side plate 121 at a position opposing the screw
receiving part 114 of the side wall 112 when the side plates 121
are mounted on the rear beam 111. A screw 136 is inserted through
the rear screw through-hole 129.
[0197] As shown in FIGS. 5, 7, 11, and 14, coupling inner
through-holes 130 are formed in the left side plate 121 at
positions corresponding to the passive coupling gears 144 of the
developer cartridges 22 in the width direction when the side plates
121 are mounted on the drum subunit 23 and the developer cartridges
22 are mounted on the drum subunit 23.
[0198] Four of the coupling inner through-holes 130 are formed in
the vertical center of the side plate 121 at intervals in the
front-to-rear direction. The coupling inner through-holes 130 are
circular holes penetrating the side plate 121 in the thickness
direction at positions corresponding to the coupling inner
through-holes 74 of the left side frame section 71 in the width
direction when the side frame sections 71 are mounted on the drum
subunit 23.
[0199] Four of center screw through-holes 132 (FIG. 11) are also
formed in the left side plate 121 at positions corresponding to the
screw receiving parts 85 of the left side frame section 71 when the
side plates 121 are mounted on the drum subunit 23. The screws 136
are inserted through the center screw through-holes 132. Four of
the center screw through-holes 132 are formed at intervals in the
front-to-rear direction and at positions between the corresponding
coupling inner through-hole 130 and shaft through-hole 124.
[0200] As shown in FIGS. 12A, 15A and 15B, the center openings 133
are formed in the right side plate 121. The center openings 133
expose the wire electrodes 80 and grid electrodes 81 provided on
the right side frame section 71 outside of the right side plate 121
in the width direction when the side plates 121 are mounted on the
drum subunit 23. Four of the center openings 133 are formed at
intervals along the front-to-rear direction. The center openings
133 are large openings shaped to fit over the fitting walls 94
including the wire electrodes 80 and capable of receiving the grid
electrodes 81.
[0201] Further, front side openings 134 are formed in the right
side plate 121 on the front side of each center opening 133. The
front side openings 134 function to expose the developing roller
electrodes 82 outside the right side plate 121 in the width
direction when the side plates 121 are mounted on the drum subunit
23. Four of the front side openings 134 are formed to correspond to
the center openings 133 and are positioned to oppose the developing
roller electrodes 82 in the width direction when the side plates
121 are mounted on the drum subunit 23.
[0202] Further, rear side openings 135 are formed in the right side
plate 121 on the rear side of each center opening 133. The rear
side openings 135 function to expose the cleaning electrodes 83
outside the right side plate 121 in the width direction when the
side plates 121 are mounted on the drum subunit 23. Four of the
rear side openings 135 are formed to correspond to the center
openings 133 and are positioned to oppose the cleaning electrodes
83 in the width direction when the side plates 121 are mounted on
the drum subunit 23.
[0203] (5) Assembly of the Drum Unit
[0204] First, the four drum subunits 23 are arranged adjacent to
each other in the front-to-rear direction. As shown in FIGS. 11 and
12A, for adjacent drum subunits 23, the front surface of the side
frame section 71 in the rear drum subunit 23 is placed in contact
with the rear surface of the side frame section 71 in the front
drum subunit 23. In this way, the drum subunits 23 are juxtaposed
in the front-to-rear direction while sloping downward and
rearward.
[0205] Next, the front beam 96 is disposed adjacent to the forward
most drum subunit 23, and the rear beam 111 is disposed adjacent to
the rearward most drum subunit 23. When disposing the front beam 96
adjacent to the forward most drum subunit 23, the front surface of
the side frame section 71 in the forward most drum subunit 23 is
placed in contact with the front sloped surface 102 of the front
beam 96. Further, when disposing the rear beam 111 adjacent to the
rearward most drum subunit 23, the rear surface of the side frame
section 71 in the rearward most drum subunit 23 is placed in
contact with the rear sloping surface 115 of the rear beam 111.
[0206] Next, the side plates 121 are disposed on both widthwise
sides of the front beam 96, four of the drum subunits 23, and the
rear beam 111 arranged in the front-to-rear direction and are fixed
to these components via the screws 136.
[0207] When attaching the left side plate 121 to the left side of
the front beam 96, four of drum subunits 23, and rear beam 111, the
front screw through-hole 128 of the side plate 121 is aligned with
the front screw receiving part 103 on the left side of the front
beam 96, and the rear screw through-hole 129 of the left side plate
121 is aligned with the screw receiving part 114 on the left side
of the rear beam 111 in the width direction, as shown in FIG. 11.
The center screw through-holes 132 of the left side plates 121 are
also aligned with the screw receiving parts 85 on the left side of
the drum subunit 23 in the width direction.
[0208] Next, the inner wall surface of the left side plate 121 is
placed in contact with the protruding ridges 84 on the left side
frame section 71 so that the left ends of the drum shafts 27 are
inserted through the shaft through-holes 124 of the left side plate
121. Simultaneously, the boss 75 of the side frame section 71 on
the left side of each drum subunit 23 is fitted into the light
transmitting through-holes 123 in the left side plate 121 such that
the bosses 75 are exposed externally in the width direction. By
fitting the bosses 75 of the left side frame sections 71 into the
light transmitting through-holes 123 of the left side plate 121,
the drum subunits 23 are restricted from rotating about the drum
shafts 27 relative to the left side plate 121.
[0209] As shown in FIG. 11, the screw 136 is inserted through the
front screw through-hole 128 and screwed into the front screw
receiving part 103, while a separate screw 136 is inserted through
the rear screw through-hole 129 and screwed into the screw
receiving part 114. Still other screws 136 are inserted through the
center screw through-holes 132 and screwed into the screw receiving
parts 85. In this way, the left side plate 121 is attached to the
left side of the front beam 96, drum subunits 23, and rear beam
111, as shown in FIG. 14.
[0210] When attaching the right side plate 121 to the right side of
the front beam 96, four of drum subunits 23, and rear beam 111, as
shown in FIG. 12A, the front screw through-hole 128 in the right
side plate 121 is aligned in the width direction with the front
screw receiving part 103 on the right side of the front beam 96.
Simultaneously, the rear screw through-hole 129 in the right side
plate 121 is aligned in the width direction with the screw
receiving part 114 on the right side of the rear beam 111.
[0211] Next, the inner wall surface of the right side plate 121 is
placed in contact with the protruding ridges 84 of the side frame
sections 71 on the right side of the drum subunits 23 so that the
right ends of the drum shafts 27 are inserted into the shaft
through-holes 124 in the right side plate 121 and the bosses 75 of
the right side frame sections 71 are fitted into the light
transmitting through-holes 123 of the right side plate 121 such
that the bosses 75 are exposed externally in the width direction.
Further, the fitting walls 94 of the drum subunits 23 are fitted
into the center openings 133 formed in the right side plate 121. By
fitting the bosses 75 of the right side frame section 71 into the
light transmitting through-holes 123 of the right side plate 121,
the drum subunits 23 are restricted from rotating about the drum
shafts 27 relative to the right side plate 121.
[0212] As shown in FIG. 12A, screws 136 are inserted through the
front screw through-hole 128 and rear screw through-hole 129 and
screwed into the front screw receiving part 103 and screw receiving
part 114, respectively. In this way, the right side plate 121 is
attached to the right side of the front beam 96, drum subunits 23,
and rear beam 111, as shown in FIG. 15A.
[0213] When the drum unit 21 is assembled as described above, the
widthwise ends of the drum shaft 27 supported in the pair of side
frame sections 71 for each drum subunit 23 are inserted into the
respective shaft through-holes 124 of the side plates 121, as shown
in FIGS. 14, 15A, and 15B. The diameter of the shaft through-holes
124 is greater than the diameter of the drum shafts 27 (the size in
a cross-section taken orthogonal to the axial direction of the drum
shaft 27) As shown in FIGS. 13A, 13B, and 13C, a portion of the
wire spring 127 crosses the shaft through-hole 124 in a diagonal
direction upward and rearward. When the widthwise end of the drum
shaft 27 is inserted into the shaft through-hole 124, as shown in
FIG. 13C, the drum shaft 27 contacts the wire spring 127 and
slightly deforms the wire spring 127 diagonally downward and
rearward. Here, in FIG. 13C, dotted lines show the shape of the
wire spring 127 before inserting the drum shaft 27 into the shaft
through-hole 124. Accordingly, the axial ends of the drum shaft 27
are urged diagonally forward and upward by the wire spring 127
toward the upper and forward contact surfaces 131 opposing the drum
shaft 27. Hence, the wire springs 127 press the axial ends of the
drum shaft 27 at a point of contact. The drum shaft 27 also
contacts the upper and forward contact surfaces 131 at points of
contact. In this way, the axial ends of the drum shaft 27 are
accurately positioned between the pairs of side plates 121 through
three points of contact.
[0214] When the drum unit 21 is assembled in this way, as shown in
FIG. 14, the coupling inner through-holes 130 formed in the left
side plate 121 oppose the coupling inner through-holes 74 of the
left side frame section 71 in the width direction.
[0215] When the drum unit 21 is assembled as described above, as
shown in FIGS. 15A and 15B, the grid electrodes 81 and wire
electrodes 80 are exposed externally in the width direction through
the center openings 133 formed in the right side plate. Further,
the developing roller electrodes 82 are exposed externally in the
width direction through the front side openings 134, and the
cleaning electrodes 83 are exposed externally in the width
direction through the rear side opening 135.
[0216] 3. Developer Cartridge
[0217] FIG. 16 is a rear view of the developer cartridge 22. Next,
the developer cartridge will be described in detail with reference
to FIGS. 2 through 6, 16, and 17.
[0218] (1) Developer Cartridge
[0219] As described above in reference to FIG. 16, the developer
cartridge 22 is configured so that the developing roller 34 is
exposed from the bottom of the developer frame 31 via the opening
36. The developing roller shaft 45 (FIG. 17) of the developing
roller 34 is rotatably supported in the side walls 141 of the
developer frame 31, with the widthwise ends of the developing
roller shaft 45 protruding from both side walls 141 in the width
direction. The electrically conductive collar members 50 cover the
widthwise ends of the developing roller shaft 45.
[0220] As shown in FIGS. 3 and 17, the windows 142 are embedded in
both side walls 141 that define the toner-accommodating chamber 37
in order to detect the amount of toner remaining therein. An
optical sensor 173 configured of a light-emitting element 174 and a
light-receiving element 175 described later (see FIG. 8) emits a
detection light for optically detecting the amount of toner
remaining in the toner-accommodating chamber 37. The windows 142
allow the detection light to pass through the toner-accommodating
chamber 37 in the width direction.
[0221] A gear mechanism (not shown) is provided in the developer
cartridge 22 on the left side wall 141. The gear mechanism is
covered by a gear cover 143 (FIG. 17). The gear mechanism includes
the passive coupling gear 144 (FIG. 17) exposed through the gear
cover 143, and a gear train (not shown) engaged with the passive
coupling gear 144.
[0222] A coupling input shaft 145 (see FIG. 5) described later is
provided in the main casing 2. The coupling input shaft 145 can be
advanced and retracted in the axial direction of the rotational
shaft 41 and can engage with the passive coupling gear 144 so as to
be incapable of rotating relative to the same. The driving force
from a motor (not shown) provided in the main casing 2 is
transmitted to the coupling input shaft 145.
[0223] The gear train includes an agitator drive gear that engages
with the rotational shaft 41 of the agitator 32, a supply roller
drive gear that engages with the supply roller shaft 43 of the
supply roller 33, and a developing roller drive gear that engages
with the developing roller shaft 45 of the developing roller 34.
These gears are engaged with the passive coupling gear 144 via
intermediate gears or the like.
[0224] As shown in FIGS. 5 and 17, a developer cartridge grip part
146 is provided on the developer frame 31. The developer cartridge
grip part 146 is disposed in the widthwise center of the developer
frame 31 on an upper wall 147 and includes a depressed part 148
formed by depressing the upper wall 147 downward, and a grip 149
provided on the rear edge of the depressed part 148.
[0225] As shown in FIG. 6, the depressed part 148 is substantially
rectangular shaped in a plan view and is formed by cutting out the
front edge part, forming a recessed part that deepens toward the
developer cartridge 22 adjacent on the front side when the
developer cartridges 22 are mounted in the drum unit 21.
[0226] The grip 149 is provided on the rear edge of the depressed
part 148 and extends in the width direction. The grip 149 includes
side walls 150 positioned at both ends of the depressed part 148 in
the width direction, and a center wall 151 that bridges the side
walls 150.
[0227] Each of the side walls 150 is triangular in shape in a side
view, narrowing toward the rear side. The side walls 150 extend
upward from both widthwise ends of the depressed part 148. The
center wall 151 spans between upper edges of the side walls 150.
The grip 149 formed in this way allows a user to insert fingers
through the depressed part 148 from the front side and grip the
inner wall surface of the center wall 151 to pull the developer
cartridge 22 upward.
[0228] The developer cartridge grip part 146 is positioned so that
the widthwise center thereof is aligned with the widthwise center
of the developer frame 31. In other words, as shown in FIG. 6, the
widthwise center of the developer cartridge grip part 146 is
positioned on the straight line X1 that passes through the
widthwise center of the drum subunit 23 in the front-to-rear
direction when the developer cartridges 22 are mounted in the drum
unit 21.
[0229] (2) Mounting the Developer Cartridges in the Drum Unit
[0230] As shown in FIG. 5, when mounting the developer cartridges
22 of each color into the drum subunits 23 for each color in the
drum unit 21, the developer cartridge 22 is first inserted from
above the drum unit 21 into the drum subunit 23 corresponding to
that developer cartridge 22.
[0231] More specifically, the collar members 50 on the axial ends
of the developing roller shaft 45 are inserted into the guide
grooves 73 formed in the side frame sections 71 of the
corresponding drum subunit 23, and the developer cartridge 22 is
pushed downward into the drum subunit 23 as the collar members 50
slide along the guide grooves 73. When the collar members 50
contact the deepest parts of the guide grooves 73, this contact
restricts the developer cartridge 22 from being pushed deeper. In
this state, the developing roller 34 is in contact with the
photosensitive drum 24. Through this process, the developer
cartridges 22 are mounted into the corresponding drum subunits 23,
as shown in FIG. 4.
[0232] When the developer cartridge 22 is mounted in the
corresponding drum subunit 23, the collar member 50 on the
widthwise right end of the developing roller shaft 45 is connected
to the developing roller electrode 82 provided on the right side
frame section 71.
[0233] Further, when the developer cartridge 22 is mounted in the
corresponding drum subunit 23, as shown in FIGS. 7 and 8, the left
window 142 embedded in the left side wall 141 of the developer
frame 31 is aligned with the boss 75 formed in the left side frame
section 71 and the light transmitting through-hole 123 formed in
the left side plate 121 with respect to the width direction to
allow passage of the detection light. Similarly, the right window
142 embedded in the right side wall 141 of the developer frame 31
is aligned in the width direction with the boss 75 formed on the
right side frame section 71 and the light transmitting through-hole
123 formed in the right side plate 121 so as to allow the passage
of detection light.
[0234] Further, as shown in FIG. 5, the passive coupling gear 144
exposed through the gear cover 143 provided on the left side wall
141 is aligned in the width direction with the coupling inner
through-hole 74 formed in the left side frame section 71 and the
coupling inner through-hole 130 formed in the left side plate 121,
allowing the coupling input shaft 145 to be inserted and retracted
therethrough.
[0235] When all the developer cartridges 22 are mounted in the drum
subunits 23, as shown in FIG. 6, the near side grip part 104 of the
front beam 96, the developer cartridge grip parts 146 of the
developer cartridges 22, and the far side grip part 116 of the rear
beam 111 are aligned in the front-to-rear direction. More
specifically, the widthwise center of these components are
positioned on the straight line X1 that passes through the
widthwise center of the drum subunit 23 in the front-to-rear
direction.
[0236] Further, when all the developer cartridges 22 are mounted in
the drum subunits 23, each developer cartridge 22 can be pulled
upward by inserting fingers through the depressed part 148 from the
front side thereof, gripping the inner wall surface of the center
wall 151, and pulling the grip 149 upward.
[0237] Hence, after mounting all the developer cartridges 22 in the
drum subunits 23 of the drum unit 21, the drum unit 21 is mounted
in the drum-accommodating section 161 described later of the main
casing 2, as shown in FIG. 1. At this time, the printer 1 can form
color images on the paper 3 according to the image-forming
operation described above.
[0238] 4. Main Casing
[0239] FIG. 18 is a perspective view showing the drum unit 21
mounted in a main casing 2 of the laser printer 1. FIG. 19 is a
perspective view of the laser printer 1 in FIG. 18 with a portion
cut out. FIG. 20 is a perspective view showing the drum unit 21
partially withdrawn from the main casing 2. FIG. 21 is a
perspective view showing the drum unit 21 after being removed from
the main casing 2.
[0240] Next, the main casing 2 will be described with reference to
FIGS. 18 through 21.
[0241] (1) Main Casing
[0242] As shown in FIG. 18, the main casing 2 has a substantially
rectangular box shape in a side view and is open on the front side.
The drum-accommodating section 161 is formed in the main casing 2
for accommodating the drum unit 21. The drum access opening 162 in
communication with the drum-accommodating section 161 is formed in
a front wall 170 of the main casing 2.
[0243] As shown in FIG. 1, a front cover 163 is provided on the
front wall 170 of the main casing 2 for covering or exposing the
drum access opening 162. The front cover 163 is rotatably supported
via hinges (not shown) provided on the lower edge of the drum
access opening 162 so as to be able to open and close over the main
casing 2. Hence, the front cover 163 can be rotated closed about
the hinges in order to cover the drum access opening 162 (closed
position) and can be rotated open about the hinges in order to
expose the drum access opening 162 (open position). When the drum
access opening 162 is exposed, the drum unit 21 can be mounted in
or removed from the drum-accommodating section 161 via the drum
access opening 162 from the front side of the main casing 2.
[0244] As shown in FIGS. 19 and 20, the rails 164 are provided in
the drum-accommodating section 161 for slidably fitting with the
flange parts 122 of the side plates 121 provided on the drum unit
21. The main casing 2 has sidewalls 165 that oppose each other in
the width direction. The rails 164 are disposed on the inner wall
surfaces of the sidewalls 165 at positions opposing each other in
the width direction and extend in the front-to-rear direction. Each
rail 164 includes an upper rail 166 and a lower rail 167 that
confront each other vertically over a gap large enough to insert
the flange parts 122.
[0245] The main casing 2 also includes the tray-accommodating
section 171 formed below the drum-accommodating section 161 for
accommodating the paper tray 7. A tray access opening 172 in
communication with the tray-accommodating section 171 is formed in
the front wall 170 of the main casing 2. The paper tray 7 described
above can be slidably inserted into the tray-accommodating section
171 in the rear direction. When mounted in the tray-accommodating
section 171, the paper tray 7 can be pulled forward and removed
therefrom.
[0246] As shown in FIGS. 1 and 19, a duct 168 is provided inside
the main casing 2 for exhausting hot air in the main casing 2 and
drawing out ozone generated by the charger 25. The duct 168 is
formed on the rear side of the drum unit 21 when the drum unit 21
is mounted in the drum-accommodating section 161. Exhaust openings
169 are formed in the duct 168 at positions facing forward.
[0247] During an image-forming operation, air in the main casing 2
is drawn out through the exhaust openings 169 formed in the duct
168, generating an airflow from the front side to the rear side
between the scanning unit 17 and drum unit 21, as indicated by
arrows in FIGS. 1 and 19. Hot air in the main casing 2 and ozone
generated from the charger 25 first rises to the space between the
scanning unit 17 and drum unit 21 and are carried along the airflow
out through the exhaust openings 169.
[0248] Since the ventilation hole 119 (FIG. 19) formed in the far
side grip part 116 of the rear beam 111 between the depressed part
117 and rear grip 118 is open in the direction of airflow, the air
can flow through the ventilation hole 119 and be exhausted through
the exhaust openings 169.
[0249] When the drum unit 21 is mounted in the drum-accommodating
section 161, as shown in FIG. 5, the coupling input shafts 145
corresponding to the passive coupling gears 144 are inserted
through the corresponding coupling inner through-holes 130 formed
in the left side plate 121 and the corresponding coupling inner
through-holes 74 formed in the side frame 71 disposed inside the
left side plate 121 in the width direction. The coupling input
shafts 145 are coupled with the corresponding passive coupling
gears 144 of each developer cartridge 22 so as to be incapable of
rotating relative to the passive coupling gears 144.
[0250] When the drum unit 21 is mounted in the main casing 2, the
end portions of the coupling input shafts 145 are inserted into
grooves (not shown) cut into the passive coupling gears 144,
thereby forming an engagement for transferring a driving force.
Further, when the drum unit 21 is removed from the main casing 2,
the end portions of the coupling input shafts 145 are extracted
(disengaged) from the grooves in the passive coupling gears 144 by
first pushing the coupling input shaft 145 toward the center of the
drum unit 21 with respect to the left-to-right direction.
[0251] In the developer cartridge 22 having this construction, the
coupling input shaft 145 transfers a driving force from a motor
(not shown) to the passive coupling gear 144, and the passive
coupling gear 144 drives the agitator 32, supply roller 33, and
developing roller 34 to rotate via the gear train.
[0252] The coupling input shafts 145 are provided in the main
casing 2 at positions corresponding to each passive coupling gear
144. The coupling input shafts 145 are extended toward or retracted
from the passive coupling gear 144 in association with the opening
and closing operation of the front cover 163. Specifically, when
the front cover 163 is opened, the coupling input shafts 145 are
retracted from the passive coupling gears 144 and, hence, uncoupled
therefrom. When the front cover 163 is closed, the coupling input
shafts 145 are advanced toward and coupled with the passive
coupling gears 144.
[0253] As shown in FIG. 8, the optical sensor 173 is provided for
each developer cartridge 22 in order to detect the amount of toner
remaining in the toner-accommodating chamber 37. Each optical
sensor 173 includes the light-emitting element 174 and the
light-receiving element 175 disposed in opposition to each other on
either side of the drum unit 21 (the light-emitting element 174 on
the right side and the light-receiving element 175 on the
left).
[0254] When the corresponding developer cartridge 22 is mounted in
the drum unit 21 and the drum unit 21 is mounted in the
drum-accommodating section 161, the light-emitting element 174 and
light-receiving element 175 are positioned on the outside of the
pair of light transmitting through-holes 123 in the width direction
and confront the light transmitting through-holes 123 in the width
direction.
[0255] With this construction, detection light emitted from the
light-emitting element 174 passes through the boss 75 fitted into
the right light transmitting through-hole 123, enters the
toner-accommodating chamber 37 via the right window 142, and passes
through the toner-accommodating chamber 37. The detection light
then exits the toner-accommodating chamber 37 via the left window
142, passes through the boss 75 fitted into the left light
transmitting through-hole 123, and is detected by the
light-receiving element 175.
[0256] The optical sensor 173 determines the amount of toner
remaining in the toner-accommodating chamber 37 based on the
frequency of detections. When the optical sensor 173 determines
that very little toner remains in the toner-accommodating chamber
37, the printer 1 displays an out-of-toner warning on a control
panel (not shown).
[0257] Terminals connected to the high-voltage circuit board (not
shown) provided in the main casing 2 are connected to each of the
wire electrodes 80 and grid electrodes 81 exposed through the
center opening 133 formed in the right side plate 121, the
developing roller electrode 82 exposed through the front side
openings 134, and the cleaning electrode 83 exposed through the
rear side opening 135.
[0258] (2) Removing the Drum Unit from the Main Casing
[0259] To remove the drum unit 21 from its mounted state in the
drum-accommodating section 161, first, the front cover 163 shown in
FIG. 1 is opened about its hinges to expose the drum access opening
162. As shown in FIG. 18, the near side grip part 104 is provided
on the near side (front side and downstream side in the pulling
direction) of the front beam 96 in the pulling direction of the
drum unit 21 (forward direction) so that the near side grip part
104 can be exposed in and operated through the drum access opening
162.
[0260] When the drum unit 21 is mounted in the drum-accommodating
section 161, the far side grip part 116 is provided on the far side
(rear side and upstream side in the pulling direction) of the rear
beam 111 with respect to the pulling direction for the drum unit
21. Hence, the far side grip part 116 is not exposed in the drum
access opening 162 when the front cover 163 is opened and,
therefore, cannot be operated.
[0261] As shown in FIG. 20, when the operator grips the near side
grip part 104 and pulls the drum unit 21 forward, the flange parts
122 are guided along the rails 164. Specifically, the flange parts
122 slide forward between the upper rails 166 and lower rails 167
as the drum unit 21 is pulled forward.
[0262] After pulling the drum unit 21 farther forward, the flange
parts 122 separate from the rails 164, as shown in FIG. 21 so that
the drum unit 21 can be pulled free from the drum-accommodating
section 161. When the drum unit 21 is pulled forward to the point
of separating from the drum-accommodating section 161, the far side
grip part 116 provided on the far side of the drum unit 21 in the
pulling direction is exposed in the drum access opening 162 and can
be gripped at this time.
[0263] Hence, when the drum unit 21 is separated from the
drum-accommodating section 161, the operator can grip both the far
side grip part 116 and the near side grip part 104 and can lift and
carry the drum unit 21 in one motion.
[0264] 5. Operations and Effects of the Drum Unit Assembly
[0265] In the printer 1 of the above described aspect, the drum
unit 21 having four drum subunits 23 can be mounted in and removed
from the main casing 2 as a unit. Therefore, the structure of the
printer 1 can prevent confusion, such as the user mistakenly
replacing a drum subunit 23 corresponding to a different color.
Further, interposing the drum subunits 23 between a pair of side
plates 121 simplifies the structure of the drum subunits 23,
thereby simplifying the manufacturing process and reducing costs.
During repair work, it is possible to replace only the drum subunit
23 requiring repair, thereby reducing repair costs. Moreover, the
structure is easy to disassemble and is convenient for
recycling.
[0266] Further, when neighboring drum subunits 23 are linked to
each other, it is conceivable that errors in positioning between
the photosensitive drums 24 accumulate. However, when coupling the
independent drum subunits 23 with the pair of side plates 121 as in
the structure of the aspect, the error in positioning of the
photosensitive drums 24 does not accumulate, thereby improving the
accuracy in positioning the photosensitive drums 24.
[0267] When the widthwise ends of the drum shaft 27 are inserted
into the respective shaft through-holes 124 of the side plates 121,
a portion of the wire spring 127 crosses the shaft through-hole
124, as shown in FIG. 13C, in a diagonal direction upward and
rearward. When the widthwise end of the drum shaft 27 is inserted
into the shaft through-hole 124, the drum shaft 27 contacts the
wire spring 127 and deforms the wire spring 127 to shift diagonally
downward and rearward. Accordingly, the axial ends of the drum
shaft 27 are urged diagonally forward and upward by the wire spring
127 toward the upper and forward contact surfaces 131. Hence, the
wire springs 127 press the axial ends of the drum shaft 27 at a
point of contact. And the axial ends of the drum shaft 27 also
contact the upper and forward contact surfaces 131 at points of
contact. In this way, the axial ends of the drum shaft 27 are
accurately positioned between the pairs of side plates 121 through
three points of contact. Therefore, the accuracy in positioning
each of the photosensitive drums 24 can be further improved.
Further, this configuration can achieve accurate positioning
through a simple structure.
[0268] Further, the side plates 121 are formed of material having a
lower linear coefficient of expansion than that of the synthetic
resin material used to form the drum subunits 23. For example, the
side plates 121 are formed of a metal or fiber reinforced resin,
and preferably a metal. Therefore, the side plates 121 can ensure
the rigidity of the drum unit 21, and can achieve more accurate
positioning for the photosensitive drums 24. Further, forming the
side plates 121 of metal or fiber reinforced resin simplifies the
manufacturing process and can reduce costs. Since the widthwise
ends of the drum shaft 27 are inserted through shaft through-holes
124 formed in the side plate 121 and positioned in contact with the
side plate 121 at the shaft through-holes 124, the side plate 121
can be used as a ground for the photosensitive drums 24 when formed
of metal. This construction eliminates the need for a special
grounding part, thereby reducing the number of required parts.
[0269] In the printer 1 of the above described aspect, the flange
parts 122 of the side plates 121 fit between the upper rails 166
and lower rails 167 of the rails 164 when mounting the drum unit 21
into or removing the drum unit 21 from the drum-accommodating
section 161 in the main casing 2. The rails 164 guide the flange
parts 122 so that the developer cartridges 22 can be slid in the
front-to-rear direction between the upper rails 166 and lower rails
167, thereby facilitating maintenance operations needed for
clearing paper jams and replacing parts.
[0270] The front beam 96 and rear beam 111 span between the pair of
side plates 121 on the front and rear sides of the drum unit 21,
respectively. Hence, the front beam 96 and rear beam 111 can
improve the rigidity of the drum unit 21.
[0271] Further, the near side grip part 104 and far side grip part
116 are provided on the front beam 96 and rear beam 111,
respectively. Therefore, the drum unit 21 can be operated by
gripping the near side grip part 104 and far side grip part 116. As
a result, this construction enhances operability.
[0272] Further, the developer cartridge 22 corresponding to each
color is detachably mounted in drum subunits 23 corresponding to
each color in the drum unit 21. Accordingly, it is possible to
replace only the corresponding developer cartridge 22 of each drum
subunit 23 to reduce running costs.
[0273] When the drum unit 21 is mounted in the drum-accommodating
section 161 of the main casing 2, the coupling input shaft 145
corresponding to each passive coupling gear 144 is inserted through
the coupling inner through-hole 130 formed in the left side plate
121 and the coupling inner through-hole 74 formed in the left side
frame section 71 provided inside the side plate 121 in the width
direction and is coupled to the corresponding passive coupling gear
144 of the developer cartridge 22 so as to be incapable of rotating
relative to the passive coupling gear 144. Therefore, this
structure can reliably drive the agitator 32, supply roller 33, and
developing roller 34 of each developer cartridge 22 to rotate by
transmitting a driving force from the motor (not shown) provided in
the main casing 2 from the coupling input shaft 145 to the passive
coupling gear 144.
[0274] Further, each drum subunit 23 has a pair of side frame
sections 71 supporting the photosensitive drum 24, and the center
frame section 72 spanning between the side frame sections 71 for
supporting the charger 25. The charger 25 can be reliably arranged
along the axial direction of the photosensitive drum 24. And the
charger opposes the photosensitive drum 24 over a prescribed gap.
This structure ensures that a reliable charge can be applied to the
photosensitive drum 24.
[0275] The developer cartridge 22 is mounted in the drum subunit 23
by fitting the collar members 50 disposed on both widthwise ends of
the developing roller shaft 45 in the developer cartridge 22 into
the guide grooves 73 formed in the side frame sections 71 of the
drum subunit 23, and by sliding the collar members 50 along the
guide grooves 73. Accordingly, the developer cartridges 22 can be
reliably mounted in the drum subunits 23.
[0276] In the right side plate 121 of the drum unit 21 described
above, the wire electrode 80 and grid electrode 81 are exposed
through the center opening 133, the developing roller electrode 82
is exposed through the front side opening 134, and the cleaning
electrode 83 is exposed through the rear side opening 135. Hence,
this structure enables a reliable connection to be performed with
each terminal connected to the high-voltage circuit board (not
shown) provided in the main casing 2.
[0277] Further, the pair of side frame sections 71, and the center
frame section 72 are all formed separately in the drum subunit 23
described above. If the side frame sections 71 and center frame
section 72 were formed integrally, a complex mold would be required
due to the difficulties in removing the components from the mold
and the molding operation would become more involved, inevitably
leading to an increase in cost.
[0278] However, by forming the side frame sections 71 and center
frame section 72 separately and subsequently assembling these
components as described above to form the drum subunit 23, it is
possible to simplify the mold structure and improve the efficiency
of molding operations, thereby making it possible to reduce
costs.
[0279] In the drum subunit 23 described above, the relative
positions of the pair of side frame sections 71 are determined
through the drum shaft 27 of the photosensitive drum 24. Hence,
since the side frame sections 71 and center frame section 72 are
assembled with the drum shaft 27 of the photosensitive drum 24 as
reference, the positioning precision of the drum shaft 27 relative
to the drum subunit 23 is improved.
[0280] Further, as shown in FIG. 15B, when assembling the drum unit
21, the bosses 75 of the side frame sections 71 for each drum
subunit 23 are fitted into the light transmitting through-holes 123
in the pair of side plates 121 for restricting rotation of the drum
subunit 23 about the drum shaft 27 relative to the pair of side
plates 121. Accordingly, the drum subunit 23 can be accurately
positioned relative to the pair of side plates 121.
[0281] Further, as shown in FIG. 8, by fitting the bosses 75 of the
side frame sections 71 into the light transmitting through-holes
123 of the side plates 121, the detection light emitted from the
light-emitting element 174 passes through the boss 75 fitted into
the right light transmitting through-hole 123, enters the
toner-accommodating chamber 37 via the right window 142, and passes
through the toner-accommodating chamber 37. Subsequently, the
detection light exits the toner-accommodating chamber 37 via the
left window 142, passes through the boss 75 fitted into the left
light transmitting through-hole 123, and is detected by the
light-receiving element 175. Accordingly, this structure can
accurately detect the amount of toner remaining in the
toner-accommodating chamber 37.
[0282] 6. Operations and Effects of the Drum Unit Mounting and
Removal
[0283] In the printer 1 described above, the drum unit 21 equipped
with four drum subunits 23 can be mounted in and removed from the
main casing 2 as a unit. More specifically, the operator can pull
the drum unit 21 from the main casing 2 so that the drum unit 21
slides along the discharge trays 64 in the front-to-rear direction
by gripping the near side grip part 104 provided on the front wall
98 of the front beam 96. The near side grip part 104 is on the near
side of the drum unit 21 in the pulling direction. Subsequently,
the operator can lift the drum unit 21 by gripping the far side
grip part 116 provided on the bridging wall 113 of the rear beam
111 in addition to the near side grip part 104. The far side grip
part 116 is provided on the far side of the drum unit 21 in the
pulling direction. Accordingly, the user need not release the near
side grip part 104 of the drum unit 21 between the step of pulling
the drum unit 21 out of the main casing 2 and the step of lifting
and removing the drum unit 21. The user also need not release a
grip on the near side grip part 104 when mounting the drum unit 21
in the main casing 2. Hence, this construction reduces the danger
of the user dropping the drum unit 21, facilitating mounting and
removal of the same.
[0284] Further, the near side grip part 104 is disposed in the
widthwise center of the front wall 98 described above, while the
far side grip part 116 is similarly disposed in the widthwise
center of the bridging wall 113 so that the near side grip part 104
and far side grip part 116 are disposed at equivalent positions in
the width direction. Specifically, the positions of the near side
grip part 104 and far side grip part 116 in the width direction are
aligned with the widthwise center position of the drum unit 21,
that is, the straight line X1 passing through the center of gravity
of the drum unit 21. Therefore, the user can easily stabilize the
drum unit 21 by gripping the near side grip part 104 and far side
grip part 116, thereby further facilitating mounting and removal of
the drum unit 21.
[0285] Further, when the drum unit 21 is mounted in the
drum-accommodating section 161, the duct 168 provided in the main
casing 2 is positioned rearward of the drum unit 21, and the
exhaust openings 169 formed in the duct 168 face forward. The
ventilation hole 119 is formed in the far side grip part 116
between the depressed part 117 and rear grip 118 in a position
opposing the exhaust openings 169 of the duct 168 in the
front-to-rear direction. An airflow formed when air in the main
casing 2 is drawn out through the exhaust openings 169 in the duct
168 (indicated by arrows in FIGS. 1 and 19) follows a direction
that passes through the ventilation hole 119. Hence, the
ventilation hole 119 reduces the amount of fluid resistance that
the far side grip part 116 applies to the flow of air. As a result,
hot air in the main casing 2 and ozone generated from the chargers
25 can follow the airflow and drawn smoothly out through the duct
168, without disturbance of the airflow.
[0286] In the drum unit 21 described above, developer cartridges 22
corresponding to each color are detachably mounted in corresponding
drum subunits 23. Accordingly, when one of the developer cartridges
22 needs replacing, it is possible to replace only the relevant
developer cartridge 22 in the corresponding drum subunit 23.
[0287] Further, the developer cartridge grip part 146 is disposed
in the widthwise center of the developer cartridge 22 at a position
in the width direction equivalent to the widthwise positions of the
near side grip part 104 and the far side grip part 116. In other
words, the developer cartridge grip part 146 is centered on the
straight line X1 passing through the center of gravity of the drum
unit 21. Therefore, when gripping the developer cartridge 22, the
user can easily find and grip the developer cartridge grip part
146.
[0288] Further, the depressed part 148 in the developer cartridge
grip part 146 is formed by cutting out the front edge of the
developer cartridge grip part 146 in a substantially
rectangular-shaped depression when seen in a plan view.
Accordingly, the depressed part 148 opens toward the neighboring
developer cartridge 22 on the front side when the developer
cartridges 22 are mounted in the drum subunits 23. The depressed
parts 148 function as a space for inserting fingers when gripping
the developer cartridge grip part 146 and facilitate the handling
of the developer cartridge grip part 146 without forming needless
space between neighboring developer cartridges 22.
[0289] Further, the near side grip part 104 provided on the front
beam 96 is disposed on the near side of the drum unit 21 in the
pulling direction when the drum unit 21 is mounted in the
drum-accommodating section 161 of the main casing 2. Therefore, the
near side grip part 104 is exposed in the drum access opening 162
and can be gripped easily. In contrast, the far side grip part 116
provided on the rear beam 111 is disposed on the far side of the
drum unit 21 in the pulling direction when the drum unit 21 is
mounted in the drum-accommodating section 161. Hence, the far side
grip part 116 is not exposed in the drum access opening 162 when
the front cover 163 is opened and cannot be operated at this time.
However, the near side grip part 104 is exposed and can be operated
while the drum unit 21 is in a mounted state, enabling the user to
grip the near side grip part 104 and pull the drum unit 21 toward
the user (forward) until the flange parts 122 of the side plates
121 disengage from the rails 164 in the main casing 2 and the drum
unit 21 separates from the drum-accommodating section 161. The far
side grip part 116 disposed on the far side of the drum unit 21 in
the pulling direction is exposed in the drum access opening 162
when the drum unit 21 is about to separate from the
drum-accommodating section 161 and can be operated at this time.
This construction restricts the drum unit 21 from being removed
from the drum-accommodating section 161 at a point between the
mounted state and the separated state, thereby preventing the user
from pulling out the drum unit 21 carelessly.
[0290] In the printer 1 described above, the front wall 170 of the
main casing 2 is provided with the tray access opening 172 in
communication with the tray-accommodating section 171, which
accommodates the paper tray 7, and the drum access opening 162 in
communication with the drum-accommodating section 161, which
accommodates the drum unit 21. With this construction, the paper
tray 7 and drum unit 21 can be removed from the main casing 2 in
the same direction, improving the operability of the printer 1.
[0291] 7. Variations of the Drum Unit
[0292] FIG. 22 is a perspective view from the left side of the drum
unit 21 (with a rotatable nearside grip part). FIG. 23 is a
perspective view showing the drum unit 21 mounted in the main
casing 2. FIG. 24 is a perspective view showing the drum unit 21
removed from the main casing 2. FIG. 25 is a perspective view from
the bottom left side of the drum unit 21 provided with front feet
110 and rear feet 120. FIG. 26 is a left side view of the drum unit
21 shown in FIG. 25. FIG. 27A is a side view of a side plate 121
illustrating the positioning of drum shafts 27 in the side plate
121 according to a first variation. FIG. 27B is a enlarged view of
FIG. 27A showing how the wire spring 127 urges the drum shaft
27.
[0293] Next, variations of the drum unit will be described with
reference to FIGS. 22 through 32C, wherein like parts and
components are designated with the same reference numerals to avoid
duplicating description.
[0294] (1) First Variation
[0295] FIG. 22 shows a possible variation of the near side grip
part 104. This variation includes mounting plates 109 fixed to the
front wall 98 of the front beam 96, hinges 108, and a grip 107
rotatably supported on the mounting plates 109 via the hinges
108.
[0296] Each of the mounting plates 109 is a thin plate
substantially L-shaped in a front view and is configured of two
pieces. One vertically extended piece is a substantially
triangular-shaped thin plate that tapers toward the top in a side
view A hole is formed through the lower portion of the
substantially triangular plate, penetrating the plate in the
thickness direction (left-to-right direction). The other piece
constituting the mounting plate 109 is bent substantially at a
right angle to the first piece from the lower end thereof and
extends outward in the width direction.
[0297] The grip 107 is substantially U-shaped in a plan view and
includes base ends confronting each other over a gap, and a free
end portion bridging the base ends. The hinges 108 are disposed at
opposing positions on the inside surfaces of the base parts.
[0298] Two of the mounting plates 109 are fixed to the front beam
96 so as to be symmetrical about the widthwise center of the front
beam 96, so as to be substantially L-shaped in a front view, and so
as to be arranged such that the holes formed in the lower portions
of the triangular plate oppose each other in the left-to-right
direction. The hinges 108 are fitted into these holes, and the grip
107 is mounted on the mounting plates 109 via the hinges 108.
Through this construction, the free end portion of the grip 107 is
rotatably supported relative to the mounting plates 109 (that is,
the drum unit 21 including the front beam 96) about the hinges 108
on the base ends. However, the base ends of the grip 107 contact
the other pieces of the L-shaped mounting plates 109 and are thus
restricted from rotating lower than a horizontal orientation.
Hence, the grip 107 is restricted to rotating about the hinge 108
within the range indicated by an arrow in FIG. 22. More
specifically, in a left side view, the grip 107 can rotate
clockwise from 0.degree. (hereinafter referred to as a vertical
state) to 90.degree. (hereinafter referred to as a horizontal
state), where 0.degree. is the upward orientation.
[0299] With this configuration, as shown in FIG. 23, the grip 107
to be gripped by the user is in the horizontal state when the user
pulls the drum unit 21 from the drum-accommodating section 161 of
the main casing 2. Hence, the pulling force is efficiently
transferred to the drum unit 21, enabling the user to smoothly pull
the drum unit 21 from the main casing 2. When the user lifts the
drum unit 21 after pulling the drum unit 21 from the main casing 2,
the grip 107 is rotated about the hinges 108 to the vertical state
shown in FIG. 24. In this way, the lifting force can be efficiently
transmitted to the drum unit 21. By gripping both the rear grip 118
of the far side grip part 116 and the grip 107, the user can easily
lift the drum unit 21.
[0300] Further, the front side grip part configured of the grip
107, hinges 108, and mounting plates 109 causes no interference
when pulling the drum unit 21 from the main casing 2, while
facilitating the user in lifting the drum unit 21.
[0301] (2) Second Variation
[0302] FIG. 25 shows a variation in which front feet 110 have been
added to the bottom ends of the side wall leg parts 101. In the
above-described aspect, the side wall leg parts 101 form part of
the side walls 97 of the front beam 96. This variation also
includes rear feet 120 disposed on the bottom ends of the side
walls 112, which constitute part of the rear beam 111.
[0303] The front feet 110 are formed continuously with the side
wall leg parts 101 and continue to protrude diagonally downward and
rearward from the side wall leg parts 101. The rear feet 120 are
formed continuously with the side walls 112 and protrude farther
downward from the bottom edges of the side walls 112 on the rear
side thereof.
[0304] As illustrated in FIG. 26, when the user places the drum
unit 21 on a desk or other surface after removing the drum unit 21
from the main casing 2, the front feet 110 and rear feet 120
contact the surface so that a gap is maintained between the surface
and the photosensitive drums 24. Accordingly, the front feet 110
and rear feet 120 can prevent damage to the photosensitive drums 24
caused by the photosensitive drums 24 contacting the surface.
Hence, this construction facilitates operations on the drum unit 21
by enabling the drum unit 21 to be placed on a desk or other
surface.
[0305] (3) Third Variation
[0306] In the drum unit 21 of the above-described aspect, wire
springs 127 urge the widthwise ends of the drum shafts 27
diagonally upward and forward toward top and front contact surfaces
131 opposing the drum shafts 27 so that the drum shafts 27 are
positioned between the pair of side plates 121 through three points
of contact. However, as shown in FIGS. 27A and 27B, the wire
springs 127 may instead be configured to urge the axial ends of the
drum shaft 27 diagonally upward and rearward toward top and rear
contact surfaces 231 opposing the drum shaft 27, similarly
positioning the drum shaft 27 between the pair of side plates 121
through three points of contact.
[0307] Specifically, as shown in FIGS. 27A and 27B, the shaft
through-holes 124 formed in the side plates 121 are substantially
rectangular in shape in a side view having sides that are parallel
in the front-to-rear direction and sides that are parallel in the
vertical direction. Accordingly, top and rear peripheral edges of
the shaft through-hole 124 follow two straight lines that intersect
at substantially a right angle and constitute the contact surfaces
231 that contact the drum shaft 27 at points.
[0308] The wire springs 127 are retained in the side plate 121
between the pair of engaging holes 126 with the center bent
downward to form a V-shape in a side view. The front side of the
wire spring 127 crosses diagonally through the shaft through-hole
124 in an upward and forward direction.
[0309] In the drum unit 21 having this construction, the wire
springs 127 that intersect the shaft through-holes 124 diagonally
upward and forward urge the widthwise ends of the drum shaft 27
diagonally upward and rearward toward the top and rear contact
surfaces 231 opposing the drum shaft 27 when the ends of the drum
shaft 27 are inserted through the shaft through-holes 124. Hence,
the widthwise ends of the drum shaft 27 are pressed by the wire
spring 127 at a point of contact and contact the top and rear
contact surfaces 231 at points of contact. Accordingly, the
widthwise ends of the drum shaft 27 are accurately positioned
between the pair of side plates 121 through three points of
contact.
[0310] Further, by setting the urging direction of the wire spring
127 diagonally upward and rearward as shown in FIGS. 27A and 27B,
the urging direction Y1 of the wire spring 127 passes through the
axial center of the drum shaft 27 in a radial direction so that
both the urging direction Y1 of the wire spring 127 and a mounting
direction Y2 for mounting the developer cartridge 22 are directed
toward the rear side of a vertical imaginary plane L1 with respect
to the front-to-rear direction. That is, the urging direction Y1 is
directed toward the same side as the mounting direction Y2 with
respect to the vertical imaginary plane L1 perpendicular to the
front-to-rear direction. Hence, the straight line Y1 of the wire
spring 127 can be set to the same side as the direction in which
the developing roller 34 presses against the photosensitive drum
24, thereby further improving the accuracy for positioning the
photosensitive drums 24.
[0311] (4) Fourth Variation
[0312] In the drum unit 21 of the above-described aspect, the pair
of side frame sections 71 and the center frame section 72
constituting each of the drum subunits 23 are formed as separate
units, as shown in FIG. 9. However, as shown in FIG. 28, it is
possible to form one of the side frame sections 71, such as a left
side frame section 71L, integrally with a center frame section
172.
[0313] In the drum subunit 23 shown in FIG. 28, the center frame
section 172 and the left side frame section 71L are integrally
molded of a synthetic resin material, while the right side frame
section 71 is molded separately of a synthetic resin material.
[0314] (4-1) Side Frame Sections
[0315] The right side frame section 71 is formed identically to the
right side frame section 71 of the aspect described above.
[0316] The left side frame section 71L is configured of a rear side
frame section 181 formed integrally with the center frame section
172, and a front side frame section 182 formed separately from the
rear side frame section 181.
[0317] The rear side frame section 181 is substantially triangular
plate shaped in a side view, growing narrower toward the top. The
front endface of the rear side frame section 181 on the upper side
forms the guide groove 73 together with the rear endface of the
front side frame section 182, described next, for guiding the
developer cartridge 22 when the developer cartridge 22 is mounted
in or removed from the drum subunit 23.
[0318] While not shown in the drawings, the drum support unit 76 is
formed in the rear side frame section 181 for supporting the
photosensitive drum 24 described above, and the axial insertion
through-hole 78 is formed in the center of the drum support unit 76
and penetrates the rear side frame section 181 in the thickness
direction thereof. One of the protruding ridges 84 described above
is formed in the upper region of the rear side frame section 181
extending in the front-to-rear direction.
[0319] A rear side recessed part 183 is provided midway in the
front endface of the rear side frame section 181, forming an arc
shape that recesses in the rear direction. Together with a front
side recessed part 184 of the front side frame section 182
described next, the rear side recessed part 183 forms the coupling
inner through-hole 74 positioned opposite the passive coupling gear
144 of the developer cartridge 22 described above.
[0320] The rear side frame section 181 also includes the screw
receiving part 85 described above positioned between the rear side
recessed part 183 and the axial insertion through-hole 78 for
receiving the screw 136 (see FIG. 29) used to attach the rear side
frame section 181 to the side plate 121.
[0321] The front side frame section 182 has a substantially
triangular plate shape in a side view and narrows toward the
bottom. Together with the front endface of the rear side frame
section 181, the rear endface of the front side frame section 182
on the upper side thereof forms the guide groove 73 for guiding the
developer cartridge 22 when the developer cartridge 22 is mounted
in or removed from the drum subunit 23.
[0322] The other protruding ridge 84 described above is formed in
the upper region of the front side frame section 182 extending in
the front-to-rear direction.
[0323] The boss 75 described above is formed on the front side
frame section 182 below the protruding ridge 84. As in the aspect,
the boss 75 is arranged so as to oppose the window 142 of the
developer cartridge 22 in the width direction when the developer
cartridge 22 is mounted in the drum subunit 23.
[0324] The front side recessed part 184 is formed in the rear
endface of the front side frame section 182 on the lower side
thereof and has an arc shape that is depressed in the forward
direction. Together with the rear side recessed part 183 of the
rear side frame section 181, the front side recessed part 184 forms
the coupling inner through-hole 74 that opposes the passive
coupling gear 144 of the developer cartridge 22 described
above.
[0325] A screw-receiving part 186 is also provided on the front
side frame section 182. A screw 185 (see FIG. 29) is screwed into
the screw-receiving part 186 for attaching the front side frame
section 182 to the side plate 121 in front of the front side
recessed part 184. The screw-receiving part 186 is cylindrical in
shape and protrudes outward in the width direction from the outer
wall surface of the front side frame section 182.
[0326] (4-2) Center Frame Section
[0327] The center frame section 172 is integrally molded with the
rear side frame section 181 described above and is integrally
provided with the center plate 86 extending in the width direction,
and the inner plate 87 (not shown in FIG. 28; see FIG. 9) provided
on the right end of the center plate 86 in the width direction.
[0328] As in above-described aspect, the charger holding unit 88 is
provided on the center plate 86; the discharge wire 28 is extended
in the charger holding unit 88; and the grid 29 is held below the
discharge wire 28. The wire cleaner 89 that grips the discharge
wire 28 is held by the charger holding unit 88 so as to be capable
of sliding in the width direction.
[0329] Further, as in the above-described aspect, the brush holding
unit 93 is provided on the center plate 86 below the charger
holding unit 88 for holding the cleaning brush 68.
[0330] As shown in FIG. 9, the inner plate 87 is formed so as to
bend from the center plate 86 on the widthwise right end thereof
and to extend forward. The inner plate 87 is substantially
triangular in shape and narrows toward the front in a side view.
The cylindrical axial insertion part 90 is provided on the front
edge of the inner plate 87 for receiving the drum shaft 27.
[0331] Further, the screw receiving parts 91 are formed in the rear
edge of the inner plate 87 at both vertical ends thereof and extend
inward in the width direction from the outer wall surface of the
inner plate 87 along the center plate 86. The screws 92 are screwed
into the screw receiving parts 91 for attaching the right side
frame section 71 to the center frame section 172.
[0332] (4-3) Assembly of the Drum Subunit
[0333] As shown in FIG. 28, the right side frame section 71 is
disposed on the widthwise right side of the center frame section
172. And the cylindrical axial insertion part 90 (see FIG. 9) of
the center frame section 172 is inserted into the receiving part 77
of the right side frame section 71. Concurrently, the cylindrical
axial insertion part 90 is aligned with the insertion through-hole
78 in the width direction The right side frame section 71 is
positioned relative to the center frame section 172 so that the
threaded through-holes 79 of the side frame section 71 is aligned
with the screw receiving parts 91 of the center frame section 172
in the width direction. Subsequently, the screws 92 are inserted
through the threaded through-holes 79 and screwed into the screw
receiving parts 91, thereby attaching the right side frame section
71 to the widthwise right side of the center frame section 172 to
complete assembly of the drum subunit 23 having a similar structure
to that in the above-described aspect. Through this assembly
process, the right side frame section 71, the center frame section
172, and the rear side frame section 181 of the left side frame
section 71L are assembled together (hereinafter referred to as the
integrated part of the drum subunit 23), while the front side frame
section 182 of the left side frame section 71L is provided
separately.
[0334] The photosensitive drums 24 are retained in this drum unit
21 as described above in the above-described aspect.
[0335] (4-4) Assembly of the Drum Unit
[0336] When assembling the drum unit 21 using the drum subunits 23
shown in FIG. 29, the front side frame sections 182 of the left
side frame sections 171 are mounted on the left side plate 121
corresponding to each drum subunit 23. In mounting each front side
frame section 182 on the left side plate 121, the front side frame
section 182 is positioned on the inside of the left side plate 121
in the width direction so that the protruding ridge 84 of the front
side frame section 182 contacts the inner wall surface of the left
side plate 121 and the boss 75 of the front side frame section 182
is fitted into the light transmitting through-hole 123 of the side
plate 121 so that the boss 75 is exposed externally in the width
direction.
[0337] At this time, the screw-receiving part 186 of the front side
frame section 182 is positioned opposite an auxiliary screw
insertion hole 187 formed in the left side plate 121 in front of
the coupling inner through-hole 130. The screw 185 is inserted
through the auxiliary screw insertion hole 187 and screwed into the
screw-receiving part 186, thereby fixing the front side frame
section 182 to the left side plate 121.
[0338] Next, the integrated parts of four drum subunits 23
assembled as described above are arranged adjacent to one another
in the front-to-rear direction. When arranging the integrated parts
of the four drum subunits 23, the rear endface of the right side
frame section 71 in the integrated part of the front-side drum
subunit 23 is placed in contact with the front endface of the right
side frame section 71 in the integrated part of the rear-side drum
subunit 23, and the rear endface in the lower part of the rear side
frame section 181 of the front side drum subunit 23 is placed in
contact with the front endface on the lower part of the rear side
frame section 181 of the rear-side drum subunit 23. With this
construction, the integrated parts for the drum subunits 23 can be
juxtaposed in the front-to-rear direction in an orientation
downward to the rear.
[0339] Next, similar to the above-described aspect, the front beam
96 is disposed adjacent to the integrated part for the forward most
drum subunit 23, and the rear beam 111 is disposed adjacent to the
integrated part for the rearward most drum subunit 23. Further, the
side plates 121 are positioned on the widthwise sides of the front
beam 96, the integrated parts of the four drum subunits 23, and the
rear beam 111 that are juxtaposed in the front-to-rear direction.
As described in the above-described aspect, the side plates 121 are
assembled to the front beam 96, integrated parts of the drum
subunit 23, and the rear beam 111 using screws 136.
[0340] When assembling the side plate 121 to the left side of the
integrated parts, the center screw through-holes 132 formed in the
left side plate 121 are aligned in the width direction with the
screw receiving parts 85 formed in the rear side frame sections 181
of the integrated parts. Subsequently, the inner wall surface of
the left side plate 121 is placed in contact with the protruding
ridge 84 of the rear side frame section 181 in the integrated parts
so that the left ends of the drum shafts 27 are inserted through
the shaft through-holes 124 formed in the left side plate 121.
[0341] Next, screws 136 are inserted through the center screw
through-holes 132 and screwed into the screw receiving parts 85,
thereby completing assembly of the left side plate 121 on the left
side of the drum subunits 23, as shown in FIG. 30. At this time,
the rear side frame sections 181 and front side frame sections 182
are arranged alternately in the front-to-rear direction, forming
the guide grooves 73 in the side frame sections 171 between the
front endfaces of the rear side frame sections 181 and the rear
endfaces of the front side frame sections 182. At the same time,
the coupling inner through-holes 74 are formed between the rear
side recessed parts 183 of the rear side frame sections 181 and the
corresponding front side recessed parts 184 of the front side frame
sections 182. In other words, the rear side frame sections 181 and
the respective front side frame sections 182 are divided from each
other in the front-to-rear direction by the coupling inner
through-holes 74.
[0342] (4-5) Operations and Effects of the Fourth Variation
[0343] By forming the rear side frame section 181 of the left side
frame section 71L and the center frame section 172 integrally, the
drum subunit 23 shown in FIG. 28 reduces the number of required
parts, thereby reducing manufacturing costs.
[0344] Further, since the left side frame section 71L is configured
of the rear side frame section 181 formed integrally with the
center frame section 172 and the front side frame section 182
formed separately from the rear side frame section 181, it is
possible to reduce the number of required parts by forming the rear
side frame section 181 integrally with the center frame section 172
and to improve the rigidity of the left side frame section 71L by
forming the front side frame section 182 separately from the rear
side frame section 181.
[0345] That is, when the left side frame section 71L is formed
integrally, the strength of the side frame section 71L is reduced
by pitting the coupling inner through-hole 74, inviting damage to
the left side frame section 71L such as cracking along the edges of
the coupling inner through-hole 74.
[0346] However, when the side frame section 71L is divided in the
front-to-rear direction by the coupling inner through-hole 74 to
form the rear side frame section 181 and front side frame section
182, the strength of the side frame section 71L is not reduced by
the coupling inner through-hole 74, thereby ensuring the strength
in the rear side frame section 181 and front side frame section
182.
[0347] Further, since the center frame section 172 is formed
integrally with the rear side frame section 181 in the left side
frame section 71L, the center frame section 172, which holds the
charger 25, can be integrally positioned with the rear side frame
section 181 relative to the side plate 121, thereby improving the
accuracy of positioning.
[0348] In the drum subunit 23 shown in FIG. 28, the left side frame
section 71L is formed integrally with the center frame section 172,
while the right side frame section 71 is formed separately.
However, it is possible to form the right side frame section 71
integrally with the center frame section 172 and the left side
frame section 71L separately. Or it is possible to form the left
side frame section 71L, right side frame section 71, and center
frame section 172 integrally.
[0349] (5) Fifth Variation
[0350] In the drum unit 21 of the aspect described above, the
developer cartridges 22 of each color are provided separately from
the corresponding drum subunits 23 and are detachably mounted in
the corresponding drum subunits 23. However, the developer
cartridges 22 and respective drum subunits 23 may be formed
integrally. In this case, it is possible to replace the toner,
developing roller 34, and photosensitive drum 24 for each color all
at once by replacing the drum unit 21.
[0351] (6) Sixth Variation
[0352] FIG. 31 is a perspective view showing a drum unit mounted in
a main casing (with a rotatable near side grip part) of a printer
according to a sixth variation. FIGS. 32A through 32C are side
cross-sectional views in a region including a front cover and a
handle, illustrating movement of the front cover toward a closed
position and rotation of the handle toward a stored position.
[0353] In the first variation described above, the rotation of the
grip 107 about the hinges 108 is restricted to the range indicated
by the arrow in FIG. 22. That is, the grip 107 can rotate from a
vertical position at 0.degree. to a horizontal operating position
rotated 90.degree. from the vertical position in a clockwise
direction when viewed from the left side. However, it is possible
to provide a stored position described next in place of the
vertical position.
[0354] Specifically, a stored position may be set to a position
indicated by a dotted line in FIG. 22 at which the grip 107 is at a
position rotated slightly (20.degree. for example) clockwise from
the vertical position of 0.degree.. Here, rotation of the grip 107
is restricted within a range from the stored position (20.degree.
position in this example) to the operating position (horizontal
position) described above. In the stored position, a force
component in the rotating direction from the weight of the grip 107
constantly urges the grip 107 to rotate toward the operating
position. Hence, if the user is not supporting the grip 107, the
grip 107 will immediately rotate from the stored position to the
operating position.
[0355] As shown in FIG. 31, storing guides 190 are provided on the
front cover 163 at positions opposing the grip 107 of the drum unit
21 accommodated in the drum-accommodating section 161. The storing
guides 190 are positioned opposite each other in the width
direction on both sides of the widthwise center of the front cover
163 and are configured of a pair of ribs elongated in a direction
orthogonal to the width direction. Each storing guide 190 is
integrally configured of a parallel part 199 extending
substantially parallel to the surface of the front cover 163 in a
vertical direction when the front cover 163 is in the closed
position, and a protruding part 200 formed continuously with the
bottom end of the parallel part 199 and protruding gently toward
the drum unit 21.
[0356] Hence, as shown in FIG. 32A, when the front cover 163 is
moved from the open position to the closed position, midway during
this movement the protruding parts 200 of the storing guides 190
contact a distal end of the grip 107 in the operating position. At
this time, the storing guides 190 apply pressure to the distal end
of the grip 107. The pressure applied by the storing guides 190
opposes the urging force of the grip 107 caused by the rotational
component in the weight of the grip 107, and the grip 107 begins
rotating from the operating position toward the stored
position.
[0357] As shown in FIG. 32B, as the front cover 163 is rotated
farther toward the closed position, the distal end of the grip 107
slides along the parallel part 199 of the storing guide 190. Here,
the storing guide 190 continues to apply pressure to the distal end
of the grip 107 in a direction for rotating the grip 107 to the
stored position.
[0358] As shown in FIG. 32C, the grip 107 completes its rotation to
the stored position when the front cover 163 has rotated to the
closed position. At this time, the storing guide 190 constantly
applies pressure to the grip 107 in the stored position.
[0359] When the grip 107 is in the stored position and the front
cover 163 is in the closed position and is subsequently moved from
the closed position toward the open position, the pressure applied
to the grip 107 by the storing guide 190 is removed, allowing the
grip 107 to quickly rotate toward the operating position due to the
urging force of its own weight described above.
[0360] With this construction, if the front cover 163 is rotated to
the closed position when the drum unit 21 is mounted in the
drum-accommodating section 161, the grip 107 rotates to the stored
position in association with the movement of the front cover 163.
Therefore, this construction eliminates the need to perform
separate operations for moving the front cover 163 and rotating the
grip 107, thereby improving the operability of the drum unit 21 and
the printer 1.
[0361] Further, if the front cover 163 is rotated to the open
position when the drum unit 21 is mounted in the drum-accommodating
section 161, the grip 107 rotates to the operating position in
association with the movement of the front cover 163. Therefore,
this construction eliminates the need to perform separate
operations for moving the front cover 163 and rotating the grip
107, thereby improving the operability of the drum unit 21 and the
printer 1.
[0362] Further, the storing guides 190 in this construction
smoothly link the opening and closing movement of the front cover
163 to the rotation of the grip 107 between the operating position
and stored position, thereby improving the operability of the drum
unit 21 and the printer 1.
[0363] 8. Variation of the Color Laser Printer
[0364] The aspect described above relates to a tandem type color
laser printer 1 for directly transferring images from the
photosensitive drums 24 onto the paper 3, but the invention is not
limited to this case. For example, the invention may be applied to
an intermediate transfer type color laser printer configured to
temporarily transfer toner images of each color onto an
intermediate transfer member from photosensitive members and to
subsequently transfer the composite image onto the paper at
once.
* * * * *